Use your normal build tools.
For e.g. 10 days:
GildedRoseTests/bin/Debug/net8.0/GildedRoseTests 10
You should make sure the command shown above works when you execute it in a terminal before trying to use TextTest (see below). If your tooling has placed the executable somewhere else, you will need to adjust the path above.
There are instructions in the TextTest Readme for setting up TextTest. You will need to specify the GildedRoseTests executable and interpreter in config.gr. Uncomment this line:
executable:${TEXTTEST_HOME}/csharpcore/GildedRoseTests/bin/Debug/net8.0/GildedRoseTests