Normally the system finds the drive with most space on it an sets the local cache.
To change it you have to change a configuration file.
Do the following
Close the program.
In fileExplorer in the path bar type %localappdata%
In there a hidden folder called RfUserData is located.
In the folder there are a file called ClientPcConfiguration.cfg.
In this file there are some JSON. On 3 different values the drive is set. There are many other values in the configuration, but don't change any of them.
Here is a example of the cache located on D:
Set this to the drive of your preference, her the cache is moved from "d" to "e" by changing the "d:" with "e:"
Then copy the RushFiles folder from the old location to the new.
Start the program again.