How do I take the slack out of a door closer chain?

Question

There is a cylinder with a spring inside. Presumably when the spring is compressed it will pull the external chain attached to it to be taught, I.e. not slack.

But I can't keep the spring compressed to then insert it back into the door cavity and faceplate on top.

Here's a sketch of what I mean by the spring inside the cylinder.

Answer 1

Looks like I need to twist the chain to increase the tension, according to this Q&A: How to stop self closing doors from slamming

Thanks to jsotola for their input.

There is another faceplate, which I had while working on this, but not shown in photograph. But, as jsotola suggests, I should check for other missing parts.

Key things:

• I was putting it in the wrong way around.

• Need to use a chain stopper, clip to hold chain while fitting.

This video was key to my understanding too: https://youtu.be/P5SalSwsigc