Apps on a chromebook are not allowed to use folders outside the app by default without permission.
Coach can use the files if they are in the app documents folder:
Copy the file “under” the app documents folder, for which Coach does not need extra permissions:
In the files app do as follows: My Files => Play Files => Documents => Coach 7 Copy the file here.
In Coach this corresponds to the user folder.
In the browser dialog click the user tab and the file should be there.