Need group date in YYYY-MM format

I hope someone can help me. I have a report where I am totaling up quantities by months. The date that I am basing it on can be either an order line date or, if it has a schedule, the line schedule date. The dates are in mm/dd/yyyy format. I created a formula for "RelDate" to determine which date to use:

IF {p21_view_oe_line.scheduled}="N"

THEN {p21_view_oe_line.required_date}

ELSE {p21_view_oe_line_schedule.release_date}

I need to change that date to format YYYY-MM and define it as a group for totals and also so it prints in the correct date order. I was able to create a date using the Month and Year functions but I need a 2 digit month, not a one digit month for January-September, for sorting purposes.

I tried using the right/left functions to extract the dates but it is looking for a string variable, not a date

I'm not too proficient at CR yet and cannot figure out how to it. Kindly advise.

Thank you very much in advance for your help!

Jan