Watch the Left Hand Tapping Scales online guitar lesson by Dmitry Lisenko from Percussive Acoustic Bass (Foundry)
First of all, if you're not familiar with the scales, you have to learn them. Next, we have to play them only with a left hand. Move your focus from notes on to the muting. The major scale starts with second finger, at the same time first finger muting the string.
It's kind of hard to control at first, but try to learn to switch your focus from the notes to muting, and remember the fingering. The same with D minor.