How to connect a Geeetech Prusa I3 Pro B to Repetier-Host on mac My y-axis is running in reverse and slamming into the front of the machine. This is not ideal for my needs.

I need to connect to it with the Repetier-Host software to fix this, and in general. This connects fine via USB, but then says Unknown printer firmw... Waiting for temperature. Sending further commands does nothing as far as I can see.

Does anyone know what I need to install to get this working?
This is not a direct answer to your question, but a solution for your problem. 

If a motor is running in reverse, there are at least 2 solutions. You can reverse the connector of the leads to the stepper, or flash new firmware where you reverse the stepper in the configuration file. 

The most effective and fast solution is to reverse the connector of rearrange the wires in the connector.