Check if the braking pads are contacting the rim in desired locations.

For the left caliper pad, marked in the red circle, loosen the bolt with a 4mm Allen wrench so the pad can be adjusted.

Align the bottom edge of the pad with the bottom edge of the braking surface and then tighten.

For the right caliper pad, marked in the yellow circle, loosen the bolt with a 4mm Allen wrench so the pad can be adjusted.

Align the top edge of the pad with the top edge of the braking surface and then tighten.