I want to add some things. On each short side of Mudi there are 3 tabs that can be hard to pop off when taking off the cover, be careful when removing it and keep in mind that the cover is held on with the tabs in reality. The screws are only to keep the cover close so that the simcard and memory card have good contact against the pins. If the tabs on the short sides snap off then its not a big deal. There are also tabs all along the long sides, but those are less likely to break and are the ones that do most of the work.
As limbot said, be careful with the u.FL connectors. Don’t use any tools to remove the wires, just your fingers. Lift up gently until the connector lifts off. When putting the connector back on, align it properly, it should not be hard to push down again into place.