How do I retrieve my messages that were sent over a year ago

Unless you have a backup from over a year ago that contains those messages, and that you can restore, you can’t recover them. If you backup on a regular basis they are gone. If you don’t backup, they are also gone.

Restoring a year old backup would be absurd, because you would be overwriting all the data on your phone from the last year with the data in the backup.