The instructions from Volvo leave out something. The cover on the interior trim panel has to pried off with bone tool or a slim screwdriver. You slide the tool under the edge to release tabs so it will slide off. I don't recall taking the window trims off to get the panel off. Does your motor run but makes ugly noise and the shaft isn't moving?
The motor works when I remove the wiper from the glass. I have applied a liberal amount of some penetrating oils to no effect. If the motor bearings are common, I can probably rebuild the motor once I get it out.
My motor quit working and after taking it out of the vehicle I found out the motor was fine but the shaft where it passes through the aluminum housing from inside to outside was so badly corroded it was binding up the shaft and wouldn't allow it to turn. Tore it apart and ran the right size drill bit through the housing by hand to cut out the corrosion and then used axle grease in there to lube it up. Reinstalled it and it runs better than ever. The fronts started to slow down and I pulled it apart and it had the same problem. It's not the motor it's the shaft binding in the housing.