Adding Comma in Duration KPI

[Asuod_]

Hello,

 I have been asked to put a comma in a duration KPI, I looked around the forums and google but could find an answer. I assume it has to be a custom formatting but unsure how to do that. On the left is what I currently have and on the right is what I'm being asked to change the KPI too. Thank you in advance. 

1500:00:00 (h:mm:ss) -> 1,500:00:00(h:mm:ss)

[brunobertels]

like this 

num(subfield('1500:00:00',':',1), '#,###.','.',',')&right('1500:00:00',6)

regards