Hello. I'm sorry you haven't received a reply sooner and I hope I can assist.
The new slave cylinder should come with a new clip installed, you then push the pipe in until it clicks which is the clip securing the pipe.
If you've taken the clip off then ideally you need to put the clip back on and push the pipe in, alternatively the clip will go on with the pipe pushed fully in.
You can usually do this with your fingers, you may need to remove the air pipe for the engine to get better access.
Let me know if I can assist further and I'll reply as soon as I'm able to.