>>8624198That flap you see covering Bee's face is the bonnet for vehicle mode, the top of chest/top needs to lock into that pice, but as you can see the toy has no clearance to pullthis off, you need to pull the bonnet back as much as possible and force the chest/top in there. The chest/top part that is forced under the bonnet is made of clear plastic, painted a yellowish orange.
Here's Cliffjumper. Unlike Bee, his piece is designed to fit exactly, so it goes in without any issue.