Search columns with similar values

Hi all,
Thanks for all the previous help.
I have a issue which has to be solved.
If column 12 has value one(1) less than column 23 then
check the next rows, if column 22 in next row has the same value as column 23 in previous row then
clear the "X" in column 6 or in column 7 or in column 8 and write "?" instead of "X".
eg:
4296076M97 in column 12 and 4296076M98 in column 23 in a row then
if 4296076M98 in column 22 of the next row then
clear "X" in column 6 and write "?" in column 6.

In need of help badly.
Thanks in Advance.