This is in the shower!
How about some pics.
Drywall protected by paint ain't gonna do it in a shower.
There is no correct way to fix it, it is just plain wrong. If you start scraping and sanding it may just all fall apart.
At the end, just before I ripped out my shower, I had plastic sheeting hung on three walls. A very
temporary solution, but kept it useable the last couple months.