Easy & Quick COBOL replace string with new from list

I need a subroutine to check variable try to find it on a list (separate file) and replace with corresponding number on the list. Each variable has corresponding number on the list. * basic programs are attached (In real program old string will be changing and not hardcoded) * in list first is 10 digit New string (always 10) followed by old string (could be anything from 1-6 digits in length)