I'm experiencing relatively slow speeds on one of my 3 Deco M4 units, as it's insisting on connecting to the main unit rather than a closer node.

My flat is quite long, and the internet access point (that my main unit is connected to) is in the main bedroom. I have a second unit in another bedroom, which has a medium signal from the main Deco (as there are two bathrooms in the way), and a third unit in the living room - essentially the three units form a straight line, albeit with bathrooms and walls in between.

I have fibre internet, and the speed on the main Deco is 500mb/s. The living room gets about 50mb/s, as the Deco unit insists on connecting to the main unit rather than the one in the middle. I imagine the speed would be similar if the living room unit connected to the middle Deco, but I'm unable to test this as I can't find a way to select the source for the living room unit.

Am I just being dense, or is there no way to manually select a signal source on the M4 unit?