If your experienced with a screwdriver and solder welt you should be ok.
If this is your first time of soldering electronics : perhaps rethink about it

Remember : a good welt is only heated about 2-3 seconds and uses a very tiny amunt of soldering tin.
and as with all electronics :
DO NOT USE FLUX (soldering fluid), it will destroy your circuit board by a chemical reaction !

Remember : This will void warranty !!!
- unscrew screws in the black plastic (do not turn the CDJ up-side-down on the platter, use wood or so to make sure all pressure is on the body of the player and NOT the platter ! Just like in my SL1200 topic you can use something like CD covers to get the desired height.
Again : KEEP THE PLATTER FREE !
- Unscrew 5 black screw from the bottom and 1 silver one on the back
- Open the CDJ like a book
- Unsolder the switch(es)
- Unscrew 6 screws of the pcb and only lift it a few cm (3-4)
- Remove the switch and replace with new original part
- put back the pcb and solder the switch to it
- then reassemble the CDJ