I am on my third TT and have fixed this problem 3 times. The first TT was easy. I was able to unscrew the end that the water sprays out of and block off all of the inside water holes. I used a piece of duct tape cut into a circle, just leaving the outside circle of holes open for water.
It worked perfect.
The second TT needed the same thing, plus it had a restrictor washer that I needed to remove.
My latest TT needed both of the previous mods, and the actual fixture had a restrictor hole that I had to drill out.
So the fix can be simple to more involved depending on just what is causing the problem.
While you are at it, now is a good time to address
The cold shot of water after using the shutoff feature.
If you don't boondock, then this probably isn't important to you.
If you do, read on.
Most TT showers will give a shot of cold water after using the shut off at the showerhead.
You get it all set for the temp you want, and turn it off to soap up, and are tortured by COLD water when rinsing.
The reason is the dribble of warm water that continues when the shutoff is engaged. In most TTs there is more resistance in the hot water supply line due to the water heater being involved. This means that the dribble of warm water will be replaced with water from the cold water line. In a few TTs the problem is the opposite, due to variations in the plumbing.
No matter, this mod will fix either situation.
Go to a hardware store and get a plastic ball cock valve. IIRC, it is the 1/2"threaded size. Get the fittings to install it between the hose and shower head. Use this as your shutoff, and the flow will be 100% stopped. When turned back on, the water will be very close to the temp it was when turned off. There will only be the natural cooling of the warm water sitting stationary in the lines.
Total cost is about $5.00 and 10 minutes.