How do i fix it? My engine has 0 compression in one cylinder?

 

Put that cylinder on TDC and do a leak down test and check where air is coming from. If from intake then you have bad intake valve, if from exhaust then bad exhaust valve, if from oil fill cap or dipstick hole then worn piston rings. It could be bent valves or any number of things. When was the last valve adjustment done?

 

With 0 information provided, I will shoot in the dark= burned exhaust valve.