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Does your master socket have 2 sockets, one for phone and one for hub, or just one socket and an external dangly filter?
In that case your extension will be wired to terminals 2&5 on the removable faceplate. Transfer those 2 wires to the data extension terminal on the backplate and then your extension socket can be used to plug in the hub. You will need to use a dangly filter at the extension to convert the phone soccket to RJ11.
There should be 2 terminals at the top left of the plate that is still fixed to the backbox.
You appear to have 2 sets of cables going to extensions, you need to identify which cable goes where and then move the wires from terminals 2&5 in the appropriate cable on the part you are holding to the 2 terminals at the top left.
Ignore the colours of the wires. Just move the existing wires as described.
The only way to tell which of the 2 cables goes where is to plug a phone into the extension socket. If you lose dial tone you have removed the wires going to that socket, if you still have dial tone, its the other 2 wires you need to move. You will need to temporarily plug the faceplate back in to check though as removing it disconnects the extensions.