Here's your two choices and I've done both. Figure out the tank dimensions, carefully cut it out, change the tank, re-install the cut piece of deck after sealing all of the edges and have a stainless steel beauty ring made and glue (marine 5200) and screw it down (stainless screws).
If not, pull the gauge sending unit/pickup tube out, suck out the tank, pull the screen, re-install and put in a nice spin on (Racore) fuel filter.... preferably a water separating filter.
Then go pray your tank doesn't get pin holes.
Is your tank aluminum?