modification of flow distance file while doing the parameters

The wiki said that it should be a minor modification for the flow direction file generated by arcgis. Could please give me a instruction of how to do this modification. Thank you so much!
Here is the link of the wiki: https://rvic.readthedocs.io/en/latest/user-guide/parameters/
In Input Files --> Flow Direction File --> 2. calculate grid box Flow Distance 