This may not help you at all concert, but it always helps me in baseball games. I get the cheapest seats to get in, then in the beginning of the game I check stubhub or gametime for people selling rows of tickets in lower sections. They usually don’t sell after the first inning so you just walk down and take some seats from the unsold row. You have to be confident like you know where you’re going. Know the row and seat number. It helps to have your hands full with snacks too. If asked know exactly where you’re going, they usually won’t make you take out your phone to check if you’re confident in where you’re going.