@tom That's really excellent news that you are working on the AT Command issue. I'm really looking forward to the update.
The thermal pad seems to be self-adhesive. When you loosen the screw it is held in place by the thermal pad.
I suspect that the thermal pad will need to be replaced if you force it off. Do you have a type designation for the thermal pad? Then I can buy a replacement somewhere.
Quectel modems are updated by plugging them into a USB adapter, connecting it to a Windows PC and installing the firmware update using proprietary Quectel software. With Sierra it probably works in a similar way.