if for some reason (mod list changes or other mods' bugs) you need to clear all your currently equipped cosmetics, follow these steps. (updated as of 4.3.0)

1. open your BepInEx folder. (if you are using a mod client, open the Mod Profile; if not, go to the PEAK game folder)
2. go to the config folder.
3. locate the config file for MultiCosmetic Mod (should be something along the lines of com.github.Spider-XD-Gaming.Multi-Cosmetic), and change the setting 'SkipCosmeticListLoading' to 'true'.
4. run the modded version of the game again, and it should clear your saved cosmetic list.