The actual removal isn't very tricky- the reinsertion is, though.
You need an incredibly thin point- a jeweler's flathead ought to work, 3/16" maybe?- and you need to depress the little detent on the side of the release. It's called the magazine catch stop. It's like the top half of a circle, and it's oriented towards the muzzle.
Depress that inwards fully, while keeping pressure on the magazine catch. As the magazine catch unseats itself (it will automatically, as its under pressure from the magazine catch spring), the magazine catch stop (the tiny bit you're depressing) is under pressure, too. Only let off gently- or it will go flying. This is especially bad because these parts are
tiny. If you drop either the magazine catch stop or magazine catch stop spring, you're in for a search to find them.
That's the entire disassembly- it's just those four parts (magazine catch, magazine catch spring, magazine catch stop, magazine catch stop spring).
For reinsertion it's the same bit. Reinsert the magazine catch (with it seated fully on the magazine catch spring), and insert the magazine catch stop (with the magazine catch stop spring inserted behind that). At this point, the details are
crucial.
The magazine catch top needs to be oriented exactly as it was when you removed the assembly- with the detent step vertical, looking at the gun from the side. If you align the catch stop improperly before depressing it and fully inserting and seating the catch, your magazine catch will be stuck. You'll require an absurdly thin implement with precise application to free it, again- or else have Sig drill out the frame.
The catch stop needs to be oriented exactly like that when you reseat it.
That ought to do it.
