A device to help fit AA45 door closers?

I would like to order some AA45 door closers to replace the ones in my flat, but I don’t know how I will be able to fit them. When I tried to remove one of the old ones it was under great tension and I broke it whilst removing.  Do they come with some kind of device that takes the tension up whilst fitting?
Yes, they come with a small metal retainer which holds the chain out while you fit it.