Modifying Axis data into hours and minutes

Modifying Axis data into hours and minutes

Hi
I would like to modify the Y-axis data into hours and minutes. How can I do that?
I create a new data column that is modifying seconds into hours and minutes, but the data type is "plain text". I think I'd need to have it in "number" in order to be able to use it in this report. 
Thanks FN