The desoldering won't be easy, but you can do it, all you need is a soldering iron and a desoldering pump (I never got solder wick to work so I don't recommend that), and the steps are heat one solder joint, keep heating and put the desoldering pump over the joint and push the button on the pump to suck the solder, be sure to not overheat the pad because that could cause it to get ripped of the board (destroyed), I will attach images for both the pump and the iron below (they don't need to be the same but they will be pretty similar)
I already have a pro soldering station and the pump... I also have a "quick" soldering paste that lowers the melting point and make it relatively easier... nevertheless unsoldering so many pins in a "delicate" environment can be a mess... the Arduino MKR is an expensive toy...
Sure, thanks. That is the first thing to do. It could probably be better to cut the pins off when they are uncovered... a long long pin to extract must be hell... twentish worse...
F