The very first character you logged in for the day (after the reset to get the next free lobi) was the one that got the mission to get the free lobi. You'll need to log back in on that first character and talk to Grym. If you can't remember which character it was, log in on each character and check your in progress missions. The mission to get the free lobi will be at the top with a checkmark indicating the mission is complete and you need to talk to Grym to complete it, which will get you the lobi.
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You have to claim the Lobi with the first char you logged in that day.