If you would rather learn how to align the rear wheel and set the drive belt tension on a M3W than a Harley, the information is in Phil Bleazeys excellent series of M3W workshop videos :
https://www.youtube.com/watch?v=1drQUxxwHWU&t=11s If you would rather read about how to do this then the M3W specific information is freely available here
https://www.mtwc.co.uk/news-post/ If the rear wheel adjustment is so far out that the belt is rubbing on the tyre, I would fix this as a priority. If the tyre sidewall is damaged it could cause a rear wheel blow out and you really don't want that to happen. Any 3 Wheeler with a deflated rear wheel is far less controllable than a 4 wheel car, many people use a puncture preventative fluid in the rear tyre to reduce the chances of this happening. It is not a side of the road job to fix a rear wheel puncture either. There should be about 3 - 6mm gap between the belt and the tyre sidewall under all conditions of drive.
