Hi, welcome to Just Answer. Sorry to hear you are having appliance trouble, I know how frustrating that can be! My name is ***** ***** I look forward to helping you!
The capacitor is a run capacitor and is optional. It is not needed for the compressor to run and is there only to help with the efficiency of the compressor while it runs. So, it goes on the run side of the relay or in between the run winding wire, depending on the type of start device you are using.
I see this is a UK model. I do not have access to the wiring diagram. I will place your question back to the list for others to see.
I see Kelly has opted out of the question so i will jump in.
Hotpoint do not list wiring digrames for the relay as they change all the time. But if you can post a picture of the relay with the wiring i will be able to tell you were the wires go from there.