Well, simple really ... trolling too fast you need a lower pitched prop. Just be aware that @ WOT with a light load it could push you up against the rev limiter. And, it might not be best for good all-around performance or fuel efficiency.
You might check a factory OEM service manual and adjust the idle speed in forward down, as usually it is a range, like 700 to 750 for example. Another thing, very popular with walleye trolling (I believe) is back trolling in reverse, which will surely slow you down by putting the stern to the forward thrust. The prop thrust is also weaker in reverse, so that helps to.
One old trick was to just throw out a 5-gallon bucket on a rope behind the boat to add drag and slow you down ... A neat tip there is to affix a 2nd longer line to the bottom of the bucket and when you need to pull it in, grab the 2nd line and haul away, as that tips the bucket over and dumps the water out.
Just for knowledge, if you haven't already, put your rig though this Prop Calculator here: https://forum.tinboats.net/viewtopic.php?f=4&t=37433 . One great advantage - if you buy a new prop - is that if you buy a Turning Point prop, you can exchange it out for a nominal fee until you get the prop performance YOU like ... so you're not stuck with a collection of expen$ive props!