Batch script to capture month & year of current & last month to pass to a command

I currently have a Windows command line tool that could change
password with the syntax:
changepw current_password new_password

I need a batch script that'll capture the last 2 digits of the year &
month & then use it as a parameter for both current_password
& new_password so that I can change the password on the 1st
of every month in a Windows Task scheduler ie:

changepw fixedportion@AABB fixedportion@CCDD
where
- AA is the last 2 digits of last month
- BB is the last 2 digits of the year of last month
- CC is the last 2 digits of current month
- BB is the last 2 digits of the year of current month

Eg:
if currently it' s Jan 2020, then
AA = 12
BB = 19
CC = 01
DD = 20

Allow me to set in the script the
'fixedportion'  so that I can it to a
string of my preference

Can't use PS / powershell script in
our place as it's disabled so Batch
script is needed