Assuming these are cable actuated disc brakes: check the cable tension. You did be able to adjust tension by using a Barrell adjuster on your brake lever. This looks like a knob between the lever body and the cable housing. Rotating it should increase (or decrease) tension.
Can you describe 'loose' more precisely? Do you mean you can pull the lever too close to the bar. Or something else?
What did you do to adjust it that fixed it?