Notes keeps deleted notes for 30 days.

1. Open the Notes app.
2. Go back to the Folders screen.
3. Tap Recently Deleted.
4. Tap Edit, select your note and tap Move, then select a folder.

If you do not see Recently Deleted, the notes might be stored On My iPhone or in another account like Gmail. Check each account listed in the Folders screen. You can also sign in at icloud.com/notes and look in Recently Deleted there.

After 30 days notes are removed for good, unless you have a device backup from before the deletion.