Suppose someone watches porn and masturbate should they masturbate less ?

Just the opposite: Not "masturbate less" but instead "watch porn less." Unlike porn, masturbation generally does not damage one's thought processes. COVID-19 lockdowns are opening up recently. Can get off the screen and do productive things offline but still wear a mask if in public. (June 2020)

Agree with Dr. Kwok: You are really focused on masturbation (as exemplified by numerous posts). Please open up your world to other things. Continue getting exercise regularly. Spend time with friends (even if remotely). Find other activities that express your creativity and give your life a sense of purpose. Expand your world beyond masturbation and exercise. It will really benefit you.

Agree with Drs F&K: Masturbation per se is not an issue. The need to watch porn and be preoccupied with mastrubation represents an unhealthy state of mind. Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV vaccine. Wish you good health!