File, folder, and database functions all run on the Developer(Agent) side of the two-system model. Here is how I would work through the manipulation of an Excel file visible on the SUT but not on the Agent:
Option 1 - Move the Excel file from its current location on the SUT into the Resources folder or some other location that is accessible from the Agent machine. This is the preferred method as it will make all of the Excel-native and the database functions available. Also, file interactions typically run faster and more reliably against the Agent. Moving the files can be done using Command Line (all OS) or File Explorer (Win). Alternately, you can use mapped letter drives or symbolic links to reach networked locations from the Agent.
Option 2 - Manipulate the Excel file directly on the SUT. This is the preferred method only when you have a brief, limited interaction with the file and are using the Excel app directly. The best example of this would be to open the file in Excel for the purpose of triggering a macro. In this case, you would treat Excel as the Application Under Test and code your script. If you need to use this method, your code might look like this:
//Presumes that code for opening Excel and opening the target file is already complete;
Click image:"Excel_NameBox"
TypeText "A2", Return
TypeText myA2_Value,Tabkey
TypeText myB2_Value, Tabkey
TypeText ControlKey,"s"
TypeText OptionKey, F4
Hope this helps,
Dave