you just need the permissions - ask an admin to turn it on for you... or do you already have the permission and there is a "bug" in the permission management?
By admin do you mean the person who created the segment? In most cases you don't have to be an admin to create a segment (permissions vary per account). Now if you want to modify a segment that was shared with you, you can't do that. You either 'Save As' the segment and modify it, which will create a new segment or ask the original owner to modify it. If the original owner is no longer an active account you can transfer the segment to your account, but an Admin will have to do that.
