I am using Turbo Tax Premier 2021 to prepare tax return. I tried to delete one of the 2555 forms but it's still there even after I hit the "Delete Form" button multiple times. Can anyone help with that?

You must remove the item that is populating the form to remove the form  ... you cannot just delete the form no more than you can get rid of a weed by just removing that you see above the  ground.  Every time you delete the form it will repopulate until you get to the "root" of the issue.