Yes you can zero the rear sight.
Sight the rifle in at 100 yards.
Hold the elevation knob TIGHTLY so it can't turn. You can use some slip joint pliers if you pad them with some leather to prevent damaging the knob.
Unscrew the screw in the knob. It's a captive screw and won't come out. DON'T try to remove it.
Pull OUT on the knob to disengage it from the splines on the receiver and turn it so the mark lines up with the 100 yard setting.
That's the line UNDER the 200 yard mark.
Push in the knob and grip it tightly so it can't turn at all, and tighten the screw tight.
To highlight the markings on the sight and knob use White Lacquer-Stik from Brownell's. This is what armorers use to fill sights and serial numbers. It's permanent, but comes out with some lacquer thinner and a toothbrush.
This is paint in a solid form. Scrape the end to expose fresh material and rub it into the markings.
Use a rag with a little lacquer thinner to wipe off the excess, leaving the markings filled.
Let dry a few hours and apply a lube to prevent rust..........
https://www.brownells.com/tools-cleaning/general-gunsmith-tools/files-engraving-tools/color-fill-lacquer-stick/