Control Mind means to Master the Mind.

To control the mind means to be the master of the mind. Controlling thoughts is usually understood as clearing out the mind of all negative and waste thoughts when they do arise. So whenever we have negative thoughts we try hard to transform them into the positive ones. Control of the mind is actually to have mastery over my thoughts, so that I am able to direct them as I wish to. So even in the most negative situations I need to maintain my positivity instead of trying hard to convert negative into positive.