my screen image is too big for my monitor; Mac

My toddler was banging away on my keyboard and has somehow managed to change the screen resolution on my Mac Mini. I *cannot* access the dock, because it is too low, and out of my view. I cannot seem to use CTRL and = or - to change the screen zoom. Also, I have an old PC keyboard, so I don't have the Apple key on it. I'm getting quite frustrated, because the only program open, is Chrome, and it has so many tabs open (that I can neither see nor close) that it is running to slow now!

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