I usually just use my hand. But you could (for example) use a small spoon to help, as long as it doesn't scratch the keyboard or damage it.
Using "P" for example: →[P]â†
You could try to "pluck" it out from either side (as opposed to from the top or bottom). You would need to apply some force, but nothing too extreme. It is more tedious, but less forceful than opening a can of soda.
And to put it back, just press it down firmly until it clicks. P, 4, 6, 8, and 0 should have similar structures underneath the cap, so you could perhaps try with one first, get comfortable with this, before you try the others.