Refitting the cap to the cylinder?

You will kick yourself when you realise how easy it is.

There will either be a locking catch to keep the two together (if you cant't see it then there isn't one) or the locking mechanism will require a twist - similar to the lid on a glass jar.

You might also kick yourself for failing to say the make & model of your machine - I don't mind - it makes it more fun trying to help you solve your problem.

Good luck...

Peccavi
June 2013