Since they are no longer on your friends list, you have to search for them manually.
: Ensure you have successfully removed them from the Blocked list in your Snapchat Settings . how to find someone you unblocked on snapchat
The most reliable way to find an unblocked user is through a manual search. Because unblocking "hides" the user from your recent chats and friends list, they will not reappear automatically. Since they are no longer on your friends
If they have deactivated or deleted their Snapchat account since you blocked them, they will not show up in search results. how to find someone you unblocked on snapchat
: Occasionally, Snapchat may prevent you from re-adding a user immediately after unblocking them. If they do not appear in search results, you may need to wait 24 hours before they become searchable again.