A WhatsApp group was deleted by the administrator (first remove all participants, then remove the group). Can I restore files in the WhatsApp group that was removed by the administrator?
If you were a group participant, then the group should still be in your phone. Although it would show that you are not a member, you should start still be able to access the old chats and media.
If you cannot find the group, then:
If you have downloaded the files, then you should be in your WhatsApp folder:
WhatsApp organizes media in different folders based on the type i.e. Audio, Video, Images, Documents.
You should be able to find the group media in one of these folders. However, this is a combined collection of all the media and you'll have to dig your way through it to find what you're looking for. There's no way to filter this media by group name.