>>1895485the barrel adjusters allow you to loosen or tighten the brake cable after its tightened in place. on your brake lever, or at the brake itself, you should see something you can turn like picrel. by setting it near center before tightening the brake cable down will allow you the most amount of adjustment. if you've got the brake to where its barely touching but seems ok otherwise, you may be able to give it a few turns to tighten it without redoing everything.
>https://youtu.be/eNxgQNOiVc0 