Your data is
Account year_month price
123456 202007 193.24
123456 202008 193.24
123456 202009 192.63
123456 202010 1454.50
123456 202011 1454.50
123456 202012 1454.50
123456 202101 1454.50
123456 202102 50.00
123456 202103 50.00
Right?
And the output desired is:
Account year_month price
789123 201902 81.19
789123 201903 82.25
789123 201904 81.64
789123 201905 10.05
I think this is kinda... Impossible? Your data is veeeery different than the desired output...