The phrase "to adjust the measurements" means to make changes or modifications to the recorded or calculated values in order to more accurately represent the correct or desired result. Full definition
I'm having a hard time understanding how to adjust the measurements for your body type, but how many yards of the fabric did you buy? (apairandasparediy.com)
Adjust these measurements if you find yourself with a bigger or smaller jar. (freeandnative.com)
Adjust measurements of ingredients to your liking / how many servings you are making. (renewingallthings.com)