Get Helix Credits for freeThe first of two ways to get Helix Credits for free is to complete the introduction quest in Assassin's Creed: Origins. You will be awarded with 200 Helix Credits when you get to the point where you leae Siwa, and these Helix Credits can be used for anything you want in the Helix Store.
If you bought the Assassin's Creed: Origins Season Pass, you will get an additional 500 Helix Credits as part of the season pass.
In total you can therefore get up to 700 Helix Credits without getting your credit card, and unfortunately it's not possible to get any more than this without buying Helix Credit packs. A pack of 500 Helix Credits will cost you about $5, while you will get 7400 Helix Credits for $50. So they are pretty expensive.
While there are few sources to get Helix Credits for free right now, keep in mind that it's possible to acquire all Helix items without spending Helix Points. Follow the link for a detailed guide to doing that.