I haven't tried focusing a CRT with two focus knobs (horizontal and vertical?), but from my general experience with focusing a CRT oscilloscope and tuning VGA signal sharpness on CRT and LCD, one good way to focus is to create three B&W images of vertical stripes, horizontal stripes, and a checkerboard. When showing the vertical stripe image, tune horizontal focus until as much of the screen as possible is in-focus. Then repeat with the horizontal stripe image and vertical focus, then double-check on a checkerboard and regular desktop usage.

I thought that the two focus knobs would be horizontal and vertical focus, but they weren’t. Not sure how they work but there are only four options to try out (increase or decrease knob 1 or 2) so didn’t take long to do.