Have a bmw right hand side water does not spray on windscreen. How to fix it.

If the left side works fine, inspect the hose going the right side. If you can take it off and retest the sprayer, you know it's not in the hose.
Clean or replace the nozzle on that side. To clean it, use a small paper clip or such to try reopening the nozzle passage.
If I was going to replace one side, I'd do both sides.
Once you're done, inspect the wash reservoir for debris or contaminants. Clean as neccassary.