Open the Notes app
Tap Folders
Check the Recently Deleted folder
Tap Edit
Select the notes you want to recover
Tap Move To
Choose the folder where you want to restore the notes
If the notes are not in Recently Deleted, check iCloud.com
Sign in with your Apple ID on iCloud.com
Open Notes
Check for the deleted notes there
Restore from an iCloud backup if available
Go to Settings
Tap your name
Tap iCloud
Tap iCloud Backup
Check the date of the latest backup
Erase and restore your iPhone from that backup if needed
Restore from a Finder backup on Mac if you created one
Restore from an iTunes backup on Windows or older macOS if you created one
Make sure Notes syncing is enabled in iCloud for future protection
Back up your iPhone regularly