Is the mirror electric or manual?
You are correct. The mirror is easy, after you have removed the door panel. I am going to give you the GM procedure in 2 separate post. One for the door panel and one for the mirror. If you get stuck at some point let me know and I will be glad to help guild you. In the first step it tells you that you need a door trim pad clip remover. This is simply a thin flat pry tool that you stick between the door panel and the door, any kind of flat pry tool will work.
J 38778 Door Trim Pad Clip Remover
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Tighten Tighten the outside rearview mirror nuts to 10 N·m (89 lb in).