You have a couple of options.1) which ever unit you want to go in reverse, get it in to reverse and then turn of the direction switch. No soldering required. 2) There are three wires connected to the motor, blue, green and yellow. I think this how you do it. Leave the green wire alone. The blue and yellow wires are attached to the brushes. Flip the wires on the brushes. You can do this and it won’t hurt anything if it doesn’t reverse the direction. But I’m pretty sure that will work. I forgot, possibly a third option - Some third party e-units have a jumper, that can change the start up sequence. If you’re using a third party you might want to check that.
Steve