How can I restore contacts?

Hello!

I'm sorry to hear you're having issues with the Contacts app.

Unfortunately if you did not back up these contacts to iCloud, you will not be able to recover them. If you did, please read this support page: Restore contacts stored in iCloud on iCloud.com - Apple Support

I hope this solves your problem!

In case you are not using iCloud contacts to sync your info, and you are creating backups on your computer, your latest backup will contain your contact information, if the backup has not been created after your contacts went missing.

But, restoring from that backup will also set back all other data to that point in time, when the backup has been made.