format text to HH:MM:SS based on condition

Hi there, I have a text column that contains "None" and time in HH:MM:SS, but sometimes the data submitted is incorrect such as H:MM:SS, instead of the correct HH:MM:SS format.  I would like a write a formula in Excel power query (perhaps a custom column) to correct the time format with one condition:

if the text in column [time of request] = None, then None, other wise format the text in [time of request] to HH:MM:SS. 

Any help is appreciated.