Redshift Community

So I have 7 slots now and I have marked them all. I wanted to re-use a slot, (ie. mark a location and save it over a used slot,) but apparently it was not possible as it said "Position has been marked".

Is there a way to re-use a slot in game?

Yes. You did it right, actually. You are always told "Position has Been Marked" if you pay attention. That or your game is glitched.