what can I do to fix this ?

 

i would take it into Maaco or some body shop....they would do a better job than you trying it at home

 

Just assuming the rest of the bumper has road wear, ect, it's not worth fixing. Just leave it, the bumper will still be secure enough. I don't think there is clearance for a plastic repair either, that area is very tight when it snaps into the rail under the headlight.

To fix it right, just buy a new, or even used bumper. A good shop would know it's not worth fixing.