During the focusing process, turning the lens makes no change to the size of the laser spot size.
This is usually caused by the lens focus ring becoming loose and not turning the lens when rotated.
Carefully unscrew the lens and remove it from the laser unit, making sure to retain the spring.
Screw on the focus ring to the lens and ensure it is as tight as possible. Be careful not to touch the glass pasts of the lens.
Re-insert the spring and screw the lens back into the laser unit.
Focus as normal.