How to calculate average by month and year

I was attempting to get help with this in Chart and Pivot table section, but I may have gotten ahead of myself. I need help with a formula to calculate the average by month and year for each customer on the list. I have enclosed a worksheet. Under Option tab, I began attempting to gather info. I figured out how to calculate the entire total for each customer using



=IFERROR(AVERAGEIF(RunningLog!B:B,Option!G1,RunningLog!C:C),0)



But cannot figure out how to break it out by month and year. Any assistance would be greatly appreciated. Thank you.
Calculate by MMMYYY.xlsx

MMMYYYAVG.jpg