Using average, offset & match together

I'm creating a fitness tracker with daily inputs & a weekly summary on a dashboard. My daily input data looks like this:

And so on. I've managed to export data from Garmin Connect and it now goes back every day for years. I want the dashboard to provide a sum of mileage and an average of intake for every 7 days. For example:

I've been trying to use a match from the 'week commencing' column in the dashboard table to identify the first day of the week in the 'date' column/source data table. Then sum/average the 7 days from that date as necessary, and put in an offset to move the reference in the source data table down 7 rows for each row the formula moves down in the dashboard table. But no luck quite yet! I hope the information provided is enough to picture what I'm going for, but I'm happy to provide a more comprehensive example of my data & desired dashboard table if required.

Imagine the following data:

Columns B:D are static values from your Garmin.

In A2:

=DROP(TOCOL(B:B,1),1)-WEEKDAY(+DROP(TOCOL(B:B,1),1),2)+1

In F2:

=GROUPBY(A.:.A;B.:.C,HSTACK(SUM,AVERAGE),1,0)