I got this:
Q: My gym bag closes with a strip a velcro and one side of the velcro is full on lint and his bag won't stay closed. What's the trick to getting the lint off velcro so it'll stick again?
A: The best way to clean velcro is with another piece of velcro. Take the rough or hook part and draw it rapidly through the lint-filled side and this will raise the trapped debris which you can pull out with your hands.
And I also found this:
Clean the Velcro if necessary by using a darning needle to lift the hair pads and duct tape to remove stragglers.