If you decide to do a fresh water dip please check the bottom of the container when you are done. Flukes are transparent and you need to place the bottom against something dark to spot the flukes!
You will need to use Prazi treatment to remove flukes. However, you also need to worry about bacteria so you need to continue trifecta. What I would do?
1) Keep fish in Trifecta for 10 days.
2) Every other day, or every 3rd or 4th day I would perform a FW dip to remove flukes. At the end of 10 day trifecta I would treat with prazi.
3) Some flukes are prazi resistant. If so, you need to use HYPO salinity treatment. I don't remember specifics but salt levels have to be dropped and stay constant. Let's figure this out later...it's in a sticky thread by Humblefish.