@_yuliana60_ Did you also buy Seasons through Steam? Are you missing anything but Seasons from your game? I haven't used Steam so I'm not sure how that is working.
EDIT: For all who might be following this thread, I was informed that Steam has been compatible with the EA app for some time.
I did find this thread about issues with content purchased through Steam.
https://answers.ea.com/t5/Bug-Reports-Technical-Issues/EA-games-bought-on-Steam-Won-t-start-with-EA-app/td-p/11914633/page/3
Back in October, @EA_Atic noted "At the moment EA games owned on Steam or Epic are not yet integrated with the EA app. You won't see that content available to you in the EA app just yet."
I don't know if that issue was resolved.
If the base game and your previously purchased content is showing in the app and showing up in your game, then you should not have to reinstall anything. Also, running a repair should not remove any of those packs that you own.
Just in case, I suggest taking some screen shots of all your owned packs as well as your purchase history in the event that you need to verify any of it.
Edit: One other thing I just read is that you should double check that your Seam and EA accounts are linked. Excerpt from the Steam store caveat: YOU MUST LINK YOUR EA AND STEAM ACCOUNTS TO PLAY; EA WILL SHARE YOUR ACCOUNT ID AND INDIVIDUAL GAME AND PLAY RECORDS WITH STEAM TO VALIDATE YOUR PURCHASE AND/OR REFUND REQUEST.
Sorry for the all caps! I'm not yelling. That's just how it's written on the site.