Check the Recently Deleted folder in the Notes app
Open Notes
Tap Folders
Tap Recently Deleted
Select the notes
Tap Move To
Choose the folder you want
Restore notes from iCloud
Go to Settings
Tap your name
Tap iCloud
Turn on Notes
Open the Notes app and wait for sync
Restore notes from an iPhone backup
Connect the iPhone to a computer
Open Finder or iTunes
Select the iPhone
Choose Restore Backup
Pick a backup that contains the notes
Confirm the restore
Restore notes from another email account
Go to Settings
Tap Apps
Tap Notes
Tap Accounts
Check Gmail, Outlook, or other accounts
Turn Notes on for the account
Open Notes and sync
Recover notes from iCloud.com
Sign in to iCloud.com
Open Notes
Check for the missing notes
Restore them if available
Check all folders in the Notes app
Open Notes
Review iCloud, On My iPhone, and email folders
Look for the missing notes
Make sure the Notes account is enabled
Go to Settings
Tap Apps
Tap Notes
Tap Accounts
Enable the correct account
Update iPhone software
Go to Settings
Tap General
Tap Software Update
Install any available update
Restart the iPhone
Turn the iPhone off
Turn it back on
Open Notes again