If you are using Python or Node.js:
Just click the ⋮ next to “Files” then click “Show hidden files”. Next click on the .replit file and finally you can change the entrypoint to whatever file you want to run.
And if you want to run the last edited file, take a look at this post:
However, you can use this method if you are not using Python or Node.js:
In the Shell, enter languagename file.fileextension. Example: java File.java or cpp game.cpp.
This method runs the output of the specified file in the Shell.