How can I repair this gouge in my Hyundia Ioniq bumper?

The clear strip is there to protect the paint on the bumper from general day to day scuffs and scrapes as you put stuff in and out of the boot/trunk. Given that it's therefore pretty expendable, I'd expect them to sell it separately - it might be listed as "trunk sill protector" or something like that.

If not, I'd suspect you can buy aftermarket strips that you just cut to the right shape for your car, intended for those that don't have one fitted as standard - it's only a bit of sticky-back plastic after all.

If you can replace the clear strip, then the problem becomes a conventional paintwork scratch, and can be fixed in more traditional methods - rub it down with sandpaper to remove any edges, fill any deep gouges with fine car body filler, sand back smooth, then repaint or touch up with the correct colour - note that there's a surprising number of shades of white when it comes to car paint, so make sure you get the right one, using the paint code from the VIN plate.

Be sure to mask off all the areas you don't want to get paint on, and try to blend the edges as you paint it - though you won't need to worry as much as normal as it'll be partly hidden by the clear strip.