Surviving Mars on Epic Games
Visit here:
https://www.epicgames.com/store/en-US/product/surviving-mars/home
Create an account or log in an already existing one, and permanently add the game on your account. Alternatively you can redeem it from the Epic Launcher on the game's giveaway page.
Scrolling even further down will show a couple of DLC's, two of them which are called:
- Surviving Mars: Mysteries Resupply Pack
- Surviving Mars: Space Race
... can also be redeemed for free once you own the base game.