"Training" Fiberglass

1) take the fender off and re-install. Sometimes a hole is out of alignment or a tweak or shim helps.
2) remove the fender and fiberglass in a steel rod or flat plate (1/8” thick or more) so when you tweak it the tweak stays put.

Fiberglass is not a factory metal fender. The molds can be off, or honestly not good at all. Worst part is the fibers in your skin. Itchy for days. Great stuff but sometimes not worth the hassle.