mm... easy fix.. but you will need a soldering iron.
Get one of those $5-10 irons.. you don't need any super soldering pro deluxe gtx xtx, since ur only fixing 1 switch..
you'd take apart the keyboard, and then just touch the iron (after hot) to the two contacts on the key to reflow the solder there.
Now, if the switch still does not work right ..
THEN you need to buy a SINGLE replacement mx blue switch, and swap it out..
You also don't need a desoldering braid or gun etc.. just take some cutips, and while the solder is melted, quickly push it up and away from the contacts using the cutip..
Don't hold the soldering iron on the contact for too long, or you might burn off the trace..
BUT, don't be afraid, because even if you burn off the trace, take a picture of the back of the board, and we will tell you where next to solder to by jumping the connection using a basic copper wire,
EVEN if you light the keyboard on fire, we can probably still fix it.. although, please don't set your keyboard on fire.
This is a straight forward jobbie, Geekhack has you covered.. Fear not.. We are here..