Power BI Power Query: Function to start from a Set date.

Hi All,

I'm sure this is pretty easy but I'm not too familiar with Power Query.

Below I have two Columns
- Index which starts from 0
- AA - This counts from 0 to 29 and then repeats every 30 rows. This starts from '0' in the Index column.

AA- = Table.AddColumn(#"Added Index", "AA", each Number.Mod([Index],30))

What I want to do is create a new column the exact same as AA but with the counting starting from 5 in the index column instead of 0. 

I've had a look around but nothing has helped so far.

Thanks in Advance.