I can’t find anywhere how to purge my stuff. because I have too many duplicates from exporting and importing.
@Kenny_Shin Welcome to the forum!
You can purge your entire (!) vault in the web vault / web app: Settings → My account → “Danger zone” → Purge vault
As already said, if you do that, you purge your entire vault and ALL items will be deleted then (and that is NOT recoverable → so at least, make a backup/export first)
Removing just duplicates is not available at the moment - there is an open Feature Request regarding that function: Duplicate removal tool/report (including merge)