The rear blower motor is not working. How do you trouble shoot and R&R Blower on 1990 Dodge Ram Van B250

I have about 12 volts at the separate rear blower switch

Asked by for the 1990 Dodge Ram Van B250
You need to check for power and ground at the blower motor with switch and key on of course.
Thanx, that was my next step. However, what is the procedure to disassemble the rear unit to get to the blower motor. It is located by the right rear door of my conversion van and I haven't been able to find any drawings or instructions.