Mistakenly deleted Notes app on iPhone how to get it back

Reinstall Notes app. If you had not turned off Notes in iCloud settings they will come back from there.

(iPhone Settings, [your name], iCloud, show all, Notes, on)

If it was turned off then they are gone unless you had a backup, but that requires restoring the iPhone.

Re-install Notes app from App Store and see.

If it shows OPEN in App Store then it is still in the phone.

Obviously wiping the phone and restoring an old backup will lose everything else since the backup date.

By the way if it was turned on in iCloud settings the data would not be in the backup.

Data is either sync'd to iCloud, or backed up, but not both