You can change some GPU settings via the nvidia-smi utility. One of them is the power cap. Perhaps this can act as a proxy to reducing the temperature? There are a number of ways to monitor the temperature using the utility, but on a quick scan I don't see a way to set a lower temperature limit directly. You might be able to do this via the desktop settings app they ship. On Windows it's in Control Panel and on Linux, it's nvidia-settings.
I'd also suggest seeing if you can get more cooling in your machine. There might be some free/open fan headers, and fans are pretty inexpensive to buy.
The relevant nvidia-smi entry is here:
SW Power Cap SW Power Scaling algorithm is reducing the clocks below
requested clocks because the GPU is consuming too much
power. E.g. SW power cap limit can be changed with