my notes in notes have disappeared. I need to get them back. How do I do this?

If you include notes in the backup (notes on my iPhone) you can restore the backup to recover the Notes. If you are using Notes with iCloud, are you sure that you have the switch turned on in Settings>Your Name>iCloud>Apps using iCloud>Notes>On.

If you restore a backup, you will overwrite the current contents on your phone with the contents in the backup.