Display duration as HH:MM:SS on Y-axis

I need to display a certain duration column (brought in to PBI as a duration type and correctly converted to decimal on load) on the y-axis with a format of "HH:MMS". The value shown will be the average of the duration over various time intervals (Year, Quarter, etc...) I've tried several suggestions found on this forum and elsewhere to no avail.  Here's a screenshot of what I have:



Thanks.