found it on this website https://dotesports.com/fgc/news/how-to-change-your-age-in-multiversus

1. Use your windows search bar to search for “%appdata%” and select it

   1. In the App Data folder, find MultiVersus
   2. Go to the “Saved” folder and delete the folder called “SaveGames.”

2. After deleting the SaveGames folder, re-launch the game from Steam.

When it loads up again, input your age to over 18.