Main fan will not turn off

I suspect you have a cooling temperature sensor issue. However, we need to start with checking for codes. I also attached a testing for the fan. First set is get codes so let's start there. Here is a guide that walks through that. If you don't have a scan tool then stop by a parts store and they can check for codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If there are no codes then I suspect we have a wiring issue causing the fan to stay on high. However, this sounds more like a command issue because the ECM thinks the temp is higher then it is actually is.