I would like see messages I deleted

If you have turned on iCloud Messages (Settings > your name > iCloud > Messages = On) then they are gone. If they are in your last backup and you merely want to look at them use a program like Backup Extractor or iMazing or something similar.

Delete a message or conversation

When you delete a message or conversation, you can't get it back. So make sure that you save important information from your messages.