The first vegvisir runestone at the standing stones where you spawn in should only show you one of the three altars for Eikthyr. Any vegvisir will only reveal the closest altar of the associated Forsaken. Interacting with runestones at altars will add that altar to your map if not already present.
If Eikthyr's trophy has already been sacrificed, just how new is this game? If someone else is hosting, they've already killed Eikthyr. (It's not hard. All you need is a spear and shield to make it an easy fight. Assuming a start from scratch, that's reasonably doable by day 3.)