Raising blue tit chick- help needed!

[kat09]

A background as to why I have this chick:
We were given the chick by some people out walking their dog near our house because they found it and asked us what they should do with it. I know that mostly it is better to leave them where they are because the parents are most likely around, but we couldn't find the nest, so decided to look after it ourselves.
We have experience with raising orphaned ducks, but this is our first bird. He is doing really well - thriving in fact, and is eating well, cleaning himself, etc. hopping about quite happily.

My Question:
We had a nest of blue tits in a gap under our roof and they all flew out for the first time today. Although our one looks a little smaller and has not tried to fly yet, he does have all his feathers coming through fast now.
So: when/how is the best way to release him? Also, do we need to try to teach him to catch insects or will he instinctively know what to do (as was the way with our ducks)?

Thanks very much for any help!