Add current date to a new column when another value is updated

Hi!

I have a list of devices with multiple attributes that I track in a table where I'm trying to insert the current date once a certain column is updated in that table.  For example, when the [Status] column value changes from any value to 'Completed', I want a new custom column [Completion Date] to populate the current date for that particular item only as a static value.  I'm not sure if I need to create a new filtered table first for all blank records in the new [Completion Date] field then run an If/Then statement to check for the conditions first?  Any help would be appreciated!