If it's just a little bit softer, you can just unscrew the barrel adjuster on your left lever a bit.

If it's way softer, you'll want to pull more cable through the anchor. It's pretty easy. Hold brake arms with left hand, unscrew cable anchor bolt a bit with right hand, then pull some more cable through with right hand (use pliers if needed), then tighten cable anchor. Check for youtube or Parktool videos on brake cable adjustment.