No offense, but you're thinking too much. It's almost a certainty that at some point in your life you jumped into water, dropped below the surface & came back up without any problem. You probably swam underwater for a short distance, maybe with your eyes open, again no problem.
While we discuss certain things as scuba skills, some are fairly instinctual & humans have been doing them automatically for eons.
Next time you're in the pool, forget about your scuba class & training. Simply drop down putting your head underwater for a few secs, then for longer (obviously holding your breath), then try to swim underwater, first level, then later even swim dow to retreive something thrown to the bottom of the pool in 5-6 feet of water (this means swimming underwater with your eyes open, which means the chlorine might sting your eyes a little, but it won't injure you) Take your time, going a little further with each effort & increasing your comfort range. Depending on how far you're removed from your childhood water experiences, you might need a few minutes or hours.
The point is get comfortable in the water, then do the scuba skills in a way that specific tasks follow what you're already comfortable with. For example, if you don't have trouble opening your eyes underwater when you don't have a mask at all, taking one off & putting it back on won't seem so difficult.