According to a comment below the video, the dose approved by WHO for Ivermectin use as an anti-parasitic is the dose doctors are using for COVID19.
The WHO dosing is:
200 micrograms/kg of body weight. That works out to 3 milligrams/15kg.
100 lb person = 9 milligrams single dose Ivermectin
200 lb person = 18 milligrams dose.

So if you weigh 150 lbs for example, 13.5 mg of the active ingredient.

The tube of stuff I am looking at contains 6.08 grams of paste containing 1.87% active ingredient.

so ,0135 gram/.0187 = .72 grams of the paste for a 150 lb person.

This is .72/6.08 = 12 % of the tube.
The tube shows calibrations for weight of the horse. Max contents says 1250 lb horse.

.12 X 1250 lbs = 150 lbs.

I guess the weights printed on the plunger correspond to human weights as well. Just set the plunger for your body weight and should be the right amount.

Disclaimer: the doc in the video said not to take meds meant for animals. I think that is just covering her liability, but I am not a doctor.

ANyhow, that is the dosage I come up with. Hope that helps.