how can I recover deleted text messages?

If you're using iCloud Syncing for Messages, your messages are not part of your back up. Once deleted, they are gone.

If you're not using iCloud Syncing, you can restore your phone from your back up.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Note that restoring a phone from a back up will overwrite everything currently on the phone.

PeggyWardlaw wrote:

How do I know if I'm using iCloud syncing

You can see what the settings look like here:

Keep all your messages in iCloud - Apple Support

PeggyWardlaw wrote:

Is there a way to backup texts and restore just them?

No.