Dealing with stuff bought cut-rate from China is really beginning to be an enormous PITN.
No direct websites, no support, no documentation, no schematics. Do you have any of these?
What I might try is measuring the voltages coming out of the 2 h-bridge motor terminals, or if
not having a DMM, connect the Tamiya motor from each motor output to ground to check for
live pins [ie pull one wire off the motor out and touch to ground]. You can power motors that way.