Yuck, a fly on your eyeball! :)
I think that almost all of the sentences sound a little off - probably because a fly landing on (and staying on) one's eyeball is rather out of the realm of possibility (flies don't tend to land on something that moves, and blinking is a reflexive action when something comes toward your eyes.) My gut feeling is that the fly will automatically fly away before you even have a chance to launch into a discussion on ways to make it go away! ;)
A fly landing in one's ear canal is much more likely... However, if you want to convey what I think you want to say, here are some possibilities:
1. Try blinking (to chase the fly away).
2. Try this if blinking doesn't make the fly go away.
Of all the sentences, "Try this if blinking doesn't work" is the best. You might also say "try this is blinking doesn't do the trick."