Click on the printer settings gears in the upper right hand area of Repetier. Printer tab, check check extruder & bed temperature.

rep2

You’ll still need to add a thermistor or small resistor (100kohm) to terminal T0 on the ramps board. This faux thermistor is to trick the board’s safety features. This can be disabled in the firmware but this makes it as easy as possible to make it a 3D printer and other functions without the need to have to re-flash different firmware (usually).

If you are going to use your Mostly Printed CNC as a 3D printer, once repetier is able to connect to your board you should have a look at the slic3r configuration, shown on this page.