I want to be able to alternate strum power chords bt i cnt seem to the hand of it especiall when its on the lower strings i always seem to hit on by accident any tips thanks
english please?

but anyways try using your fret hand to help mute the strings you dont want to hit
Lightly lay your index finger back to mute strings you don't want to hit

And for power chords on the 5th string root, use your index finger as well to touch the 6th string to mute it out