I'm not sure I understand your objective so I'll outline a scenario to explain the workflow for the tool.
You have defined a chain in COGO and through some editing process it now has equations that you don't want. Your goal is to re-station the chain to remove all the equations so the stationing is uniform from start to end.
Load the tool and select the chain. Enter the station value for the start of the chain. You also need to specify which element of the chain to apply the stationing from. In this case we want to station from the beginning. To determine which element to specify, run the Describe tool to report the chain in the COGO window, then scroll to the beginning and note the name of the first element of the chain. In most cases it will be a point, so you would specify that point in the dialogue.