You can only use a scroll of tarrasque summoning once.

Wizards can't copy non-spells into their spellbook...

The wizard's rules for copying a spell into a spellbook are detailed in the "Your Spellbook" sidebar, below their Spellcasting feature:

Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.

Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation.

For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells.

I won't bother bolding it, but the word "spell" obviously appears throughout this subsection of the sidebar, including in the name of the subsection itself. The only things that wizards can copy into their spellbook in this way are spells.

...And the scroll of tarrasque summoning doesn't contain a spell.

The description of the scroll of tarrasque summoning magic item states (Icewind Dale: Rime of the Frostmaiden, p. 315):

Scroll, legendary

Using an action to read the scroll causes the tarrasque (see the creature's entry in the Monster Manual) to appear in an unoccupied space you can see within 1 mile of you. The tarrasque disappears when it drops to 0 hit points and is hostile toward all creatures other than itself.

That's all it says. At no point in its description does it mention any spell; it is simply a magic item of the "scroll" type, of legendary rarity, and using an action to read it causes the tarrasque to appear. (The description references the tarrasque's entry on MM p. 286, which notably states, "It is widely believed that only one of these creatures exists, though no one can predict where and when it will strike.")

According to D&D Beyond's magic item listing, the scroll of tarrasque summoning is one of only two published magic items of the "scroll" type outside the DMG, both of which appear in the Icewind Dale: Rime of the Frostmaiden adventure - the other one being the scroll of the comet on p. 315. (The DMG only contains one type of magic item scroll that's not a spell scroll: the scroll of protection.)

As such, the scroll of tarrasque summoning is a scroll, and thus obeys the rules for scrolls on DMG p. 139 (under the "Magic Item Categories" section):

A scroll is a consumable magic item. Whatever the nature of the magic contained in a scroll, unleashing that magic requires the user to read the scroll. When its magic has been invoked, the scroll can’t be used again. Its words fade, or it crumbles into dust.

However, it is not a spell scroll and does not say it contains a spell, so it can not be copied into a spellbook by a wizard for reuse. (The same is true of a scroll of protection, or a scroll of the comet.) As such, based on the rules, I don't know of any official way for a character to use a single scroll of tarrasque summoning more than once.

We don't have enough information to know

The item description is a teaser for an as yet unreleased book. We don't even know if that is the complete description of the item or if there is more restrictions.

All we really have to go on is the follow up tweet:

Not a spell scroll. #wotcstaff

So it is unlikely this item will obey the standard rules for spell scrolls. Perhaps it is already multiple use, since the item also doesn't say it is destroyed after use. Though it likely follows the general rule for scrolls:

A scroll is a consumable magic item. Whatever the nature of the magic contained in a scroll, unleashing that magic requires using an action to read the scroll. When its magic has been invoked, the scroll can't be used again. Its words fade, or it crumbles into dust.

Notably it does say "the tarrasque" meaning it is a singular creature and, even if you could cast it multiple times, it is highly unlikely that that it would allow multiple tarrasques to exist. But in theory if you could cast it multiple times you could keep moving the Tarrasque around as an action every turn.

We simply don't know enough about the item to make an informed ruling at this stage.

The only parallel to this item is the Scroll of Protection from the DMG. It, like this item, is listed as a scroll but isn't a spell and doesn't appear on any spell list. According to this question it also obeys the standard rule for scrolls and is a single use magic item.

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^{This answer will be outdated following the release of the Icewind Dale: Rime of the Frostmaiden. If I haven't already updated it feel free to leave a comment to remind me.}