I would like a script when the value is changed in the worksheet then it
completes the following taste. If Column D or Column E are blank then search
to see if the values in Column A and Column B have matching values from other
rows in the worksheet then fill in the missing values for Column D or Column
E.

This so much for the help.

Thanks,

Example:

Column A Column B Column C Column D
128 654 DRFT HJKO
245 879 FGHT KLTY
128 654
234 345 HJUY DSGT

Desired Output:
Column A Column B Column C Column D
128 654 DRFT HJKO
245 879 FGHT KLTY
128 654 DRFT HJKO
234 345 HJUY DSGT