Rename your existing files. Do not delete them.
Change repentance.save.dat to repentance.save.OLD.
Do the same for repentance.save.dat.backup.
Before we hand over the link, let’s define the prize. A Dead God save file is a repentance.save or rep_persistentgamedata file that registers 100% completion in the game’s stats. Specifically, it includes: the binding of isaac repentance dead god save file link
Steam Cloud will try to "correct" your new save. Turn it off: Rename your existing files