Leading zeros for alphanumeric column

Hi,

I have a column with alphanumeric value. Some of the values are 5 digits, I would like to create a new column and add leading zero to make it all 6 digits.

I am using below but its giving me error as the column contains alphanumeric value and is in text data type 

= Table.AddColumn(#"Previous Step", "Leading 0s", each Number.ToText([C_ColumnAlphaNumeric], Text.Repeat("0",6)))

How can I add leading zeros column?

Thanks,

Daven