Step 1: Repair Kit
You should have received a repair kit in your original packaging. If you have lost it you can purchase on from here.
Step 2: Prepare
Find the tear and select the correct colour cotton to match. If the tear is large consider using one of the patches in the kit.
Step 3: Stitch
Carefully stitch over the tear or around the patch to seal the tear.
Step 4: Inflate
Now inflate the castle and check that there is no air leaking through the seal.