This is only available on Android devices at the moment.
You can access the feature by tapping on the “Free gold!” button in the universe scene or by tapping the “Offers” button in the Store.
From the tutorial inside the Offerwall:
Step 1: Choose an offer
Step 2: Complete the requirements
Step 3: Enjoy the free rewards
Once you have started an offer it should appear in the “In Progress” tab inside the Offerwall interface.
The status should be upgraded to “Completed” once the offer is done.
Once the requirements are complete you can go back to lemmings and receive the rewards. Note that both apps (the one from the offerwall and lemmings must be connected to the internet).
I haven’t received my gold!
If you believe you have fulfilled all of the requirements and have not received your reward, please allow up to 24h for the gold to appear. If you still don’t receive the reward, please contact us using the support button in the in-game menus.