In your photo just above the fuel filter is the lift pump on the engine block. The hose leaving the lift pump goes into the top of the injector pump very near to where the arrow points. That's where you bleed air if needed. I doubt you will need to bleed the system if you refill the fuel bowl/filter. Put the filter back on, but don't tighten the top ring. Open the petcock until fuel spills out from the filter ring and tighten the ring until fuel stops running. Wipe up the excess fuel and I'd bet your tractor will start right up and run fine without ever needing to bleed it.
BTW: My manual says that the fuel system (almost identical to yours) is self-bleeding and rarely ever needs manual bleeding. However, you have located the inlet bleed point and the outlet bleed is by loosening the injector fuel line retaining nuts and let air out of each injector. Again, I'd bet you'll not need to do this.
