Site Explorer -> Organic Search -> Organic Traffic -> Average Traffic between two intervals (ex. Show average Organic Traffic between June 2019 and June 2020).

I think you can solve this either by:

a) adding up all organic traffic values in a day/month (n) and diving them by that number n, or

b) Using a formula for finding average value of a given function f(x), over an interval from a to b (ex. https://www.mathopenref.com/calcaveval.html)

Thanks. :)