How can I install a kickstand spring on a 88 Harley Sportster?

If your problem is that you cannot stretch the spring enough to reach the holes on the kickstand as well as the small hole under the motor, you might try taking the kickstand off by removing the 1/2" bolt from the top of it, thread the spring into both holes and now you should be able to get the leverage necessary to stretch the spring and put the kickstand back into its mounting hole and the bolt back in.