Mechanical Keyboards

One way might be to flush it with a spoonful of 99% IPA^[https://en.wikipedia.org/wiki/Isopropyl_alcohol], followed by some wiggling and then using a compressed air-can to push wind into it from one direction, causing the IPA and the dirt mixed with it to come out of some gap in the opposite direction.

Since it is the Ctrl key (hoping it to be in the a corner as it usually is), you can tilt the keyboard such that the Ctrl key is on the bottom, then pour IPA on the higher corner of the key, such that it drenches the PCB under the key while flowing down and while you wiggle it. And then again, spray from the higher point, such that the exhaust is in the direction of the edges and corners, reducing the dirt that might transfer to other keys.

However, you might want to check just in case the back is removable. That should make stuff easier as you then won't require guessing which way the dirt solution might go in a closed box.

Either way, keep it for a while after you do the thing and before plugging it in (right, you need to unplug it first), so that most of the IPA is evaporated before you start it up.
Keyboards tend to be much simpler as compared to stuff like motherboards, so I'd guess using a hair dryer instead of compressed air should be fine too (just don't turn on the heat).