I bet it's held in %1. In a batch script, the replaceable parameter %1 contains the first (or only) parameter passed to the script. If it contains a valid file name, it can be modified with the standard variable modifiers (see the FOR documentation for details - type FOR /? at the prompt) ~d is drive, ~p is path, ~n is name, ~x is extension.
%1 is the raw parameter
If it is a file name, it may already hold the full drive and path, but you can check with simple tests
echo %1
echo %~d1
echo %~p1
echo %~n1
echo %~x1
They can be combined:
echo %~dpnx1
Passed to a variable:
set parameter=%1
echo Parameter is: %parameter%
(etc)
So try that & report results if you need further help.