When you say slim I guess you mean that your keyboard is TKL (ten key less), look it up if you don't know what it's.
Regardings opening your keybaord that shouldn't be such a big deal. If you have looked at any video where a modern keyboard gets dissasembled you should be fine, probably any ducky board is close enought. It's just a couple of screws.
When you have opened the case it comes to see if the switches are plate or PCB mounted, as before look it up if you don't know the diffrence, it differs how they are attatched. From my search on the interwebs it say it's plate mounted.
Remove the not functional switches, requires soldering, and clean them up. Don't forget to also clean the PCB. Solder the switches back and and see if it helped, if not get new ones.
If you don't have any soldering iron or any knowlegde it might just be easier and cheaper to get a new one. If you don't know how to do it you might have some friend / family with the skill and equipment.
Good luck.
