...
/reg/g/pcds/dist/pds/x.x.x/build/ami/bin/x86_64-linux-opt/offline_ami
where x.x.x should be the most version in the pds directory (3.3.1 5 as of this writing).
Click the Select button and the program will bring up a "Select Directory" dialog. Use that to navigate to the directory containing the xtc files you are interested in. For example:
...