They are soldered into place, so unless you can do logic board repair its not going to be one you can do, as I pretty much guarantee you'll end up pulling pads when you remove the old port from the board.
First thing id do is get a microscope or magnifying glass and check you have nothing in the charge port at the back. Then check if you have any broken or bent pins inside the charge port.
If the charge port looks ok its unlikely that its the port, its not like the iphone ports that have components on them, the ipad flex is basically just a wire with a plug on the end so not really much that can go wrong with it.
If its not the charge port its going to be a component on the motherboard, so you need to speak to someone in your area that does logicboard repairs.
The mini 2 does have the same piece of cr*p power management chip the air 1 also has which does suffer from charging problems, so could be fun to fix if thats the case.