Without a backup? There is no quick. But you can take steps to prevent this from happening in the future. Profile and following wipes do occasionally happen. Hence, add this relay to your general app relays wss://hist.nostr.land then, if you ever need to restore go to

nostr.land

Restore your follow list

A tool to easily restore your follow list.

You can also make manually backups (and maintain your contacts) @

Plebs vs. Zombies

Plebs vs. Zombies | Nostr Follow Manager

Clean up your Nostr follow list by identifying and removing dormant zombie accounts. Hunt zombies, manage follows, and keep your network alive!