My 15-22 is placing most shots in the 8 ring [3" low]. I should lower the dot to raise the point of impact, right? This is at 40 yards at the range. My left hand gets shaky after the first few shots, and this is offhand shooting. I'm 79. Any other old geezers having one hand shake while the other remains steady?

Without knowing what red dot you have, I am going to make the assumption that the elevation knob is marked for indicating the direction you would like to move the point of impact...

So, since your POI is low, you would want to move it up by turning the dial in the direction indicated for up. The direction indicated on the knob refers to the direction to move the POI on most red dots that I have experience with.

Easy to remember which way to go: FORS:Front-opposite, Rear-same. (a red dot is considered a rear sight)

I have a UTG red dot with a cantilever mount. Considering a better red dot. The Vortex Strikefire or the Bushnell AR Optics 1x MP Illuminated Red/Green T-Dot Reticle Riflescope. Any experience with these two? I hate to give up the cantilever mount, but I can't seem to get the UTG sighted in.

I think with a red dot, it's even simpler. Line it back up with the dot where you had it, then move dot to where the hole was.

So, like the method above, if you're shooting low, move the dot down.

Yes, moving the dot down is the same as moving the POI up. But the POI method description was from using a scope. I usually describe the red dot method as making the dot chase the POI. In a scope the target background moves up or down and the crosshair stays the same so it looks like you are raising the target. In a red dot the dot moves and the target stays the same so it looks like you are dropping the dot. Either way does exactly the same thing but in the context of the type of optic you are using it makes a difference because of what you are seeing thru the optic.

If your irons are zeroed just move the dot accordingly.

Most if not all red dots have the adjustments labelled for which direction you need to move the point of impact.

For example, if the dot is on the bullseye and your shots are grouping consistently low and center, you would turn the adjustment in the direction marked for "up"

Thinking about which way the dot is actually moving in relation to where it was is unnecessary. Good to know for a mental exercise, but not practical in achieving your goal, because you still would be faced with an adjustment marked as "up" but does not refer to actually moving the dot up, because as others have mentioned, if you do all the figuring and decide you need to move your dot up, you would turn the adjustment in the "down" direction anyway.

tl,dr- Up/down and left/right indications on the adjustments on red dots are referring to the direction the point of impact will shift