If I understand you correctly, you're trying to apply the Forgemaster archetype to a character but you don't see the archetype listed. Is that correct?
If so, first make sure that you've purchased the Advanced Race Guide data package, as that is the book where the Forgemaster comes from.
If you've bought and installed the data package but still don't see the archetype, make sure that you've re-activated your license (this is how your copy of HL "learns" what new packages you have). After that, check the "Configure Hero" menu (shortcut is CTL-K) and make sure that you have "Advanced Race Guide" checked.