Where can I purchase an extra builder for this game?

Builder VS worker is diff

An extra worker comes in a growth pack and is available in the growth store! It's different from a builder that builds the buildings, the worker clears objects around the base as you open new areas, you'll be offered an extra working during the upgrades to your base, so you don't have to look for one! A builder is different abd you will be offered one of these too on a pack while you build your base as far as I am aware the maximum builder is two! The workers have 6

what to do when it says one of my two builders (not workers) is locked. apart from buying a bundle that is
now I can only build once at a time you can imagine how that sucks