How to change Bethesda account in Doom Eternal?

Issue is caused by Bethesda faulty DRM. If provided with non existing account, it will create one. When linking via Steam in-game browser DOOM Eternal stripped underscore from email which caused DRM to link Steam to invalid email.

There are two options to recover from this mess, and both are imperfect. Solution are not limited to Steam, linking to Playstation, XBox, and Nintendo, accounts works the same (according to Bethesda Support).

• relink Steam/Console to valid account, which might result in loss of Additional Content
• change email in invalid account to access it, which will be a problem if you have something linked to your valid account

Both actions require Bethesda support assistance. Both will require proving ownership of linked account, in Steam case I needed screenshot of purchase note (transaction ID) and username.

Additional Content is:

Fallout 76 - All Game Progress Data, this includes characters, purchases and Fallout 1st membership.
Skyrim / Fallout 4 - Only Creation Club purchases/Mods
Rage 2 - Unlocked event skins and bonus content
The Elder Scrolls: Legends - All Game Progress Data
Quake Champions - All Game Progress Data
The Elder Scrolls: Blades - All Game Progress Data
Wolfenstein: Youngblood - Unlocked skins
DOOM Eternal – Battlemode / Battlepass progress, Pre-order content, Deluxe Edition content
Slayers Club - All points and activity

Bethesda Support confirmed that relinking Steam/Console will result in Year One Pass:

If you accept the unlink request the you will lose the following DOOM Eternal content

DOOM Eternal – Battlemode / Battlepass progress, Pre-order content, Deluxe Edition content Slayers Club - All points and activity

The Deluxe Editon content is Year One Pass (Includes DLC 1 & 2), Demonic Slayer Skin, and the Classic Weapons Sound Pack together.

Once Support changes email in Bethesda account to which your game is linked, you just have to confirm email.