Where can i ask re asm programming problem with bcd subtraction

As per title. I know this is pbp forum but I can't seem to find a suitable forum to ask a question ref assembly language.

I have a 10 digit number stored in 5 byte variables as packed BCD representing a frequency. Say the number is 10000000 in freq4, freq3,freq2,freq1,freq0 whre freq4 is MSB

I want to subtract 9000000 from this 10 digit number. The number would never be less than 9000000. This would be an if offset for a ham radio.

I have tried but the result always screws up the result with unfortunately no way of debugging my efforts.

Thanks for your time.