In a country like Blairstrip 1 you need a good raincoat and DoomMeisters favourite one has a broken zip. Rather that buy a new one as the corporate overlords would have us do, or indeed to fully replace the zip DoomMeister will repair the missing tooth using his awful sewing skills and a piece of a cotton bud (Q-Tip).
Step 1: Reassemble the Zip
Push the slider as far away as possible from the missing tooth whilst you are working.
Step 2: Fashion An U Piece
This U piece will not help the zip stay together, hopefully there are already enough teeth for this but will prevent the slider coming away again.
Step 3: Sew the U Piece in Position.
When you have tested the repair to check that it works and the slider does not foul on the repair then you can make it double permanent by covering your new sewing with cyanoacrylate adhesive (superglue).