You need SQL. Are you sure you mean version 4.2? That is very old. If you have interactive SQL, you do the following (try this out on a test system or file beforehand!):
1. Get a command line.
2. Take backup of your file. For example:
CPYF YOURLIB/YOURFILE BACKUPLIB/YOURFILE CRTFILE(*YES)
3. Type STRSQL and press <Enter>.
If you don’t have interactive SQL you’ll need to stop here.
3. Otherwise, you need an SQL UPDATE, like so:
UPDATE <tablename> SET fieldA = ‘New Salesperson’ WHERE fieldA = ‘Old Salesperson’
Then press <Enter>.
Be very careful with SQL. If you don’t put in the WHERE clause, you will update the whole table.