remove the arm inspect the taper-- look at the arm--- if the aluminum is completely mushroomed-- replace the arm--- check the length and angle--- if it looks kinda Ok-- use a washer and grease the bolt and put it back on--
the washer should sit behind the head of the crank bolt and the lip of the inner arm --- if you are stripping the bolt or the treads on the spindle STOP-- remove and get new....my best shot-- not fact! I assume this is a square taper--- I did this once on an old bike it seemed to work.... that washer forces the arm a bit closer to the stay--- watch carefully