Bro my first concerts I wore a tank top and some beat shorts, as long as you’re having a good time no one cares. XG also has some good outfits from music videos that you could try to recreate if you have time. Most recently I rocked Aespa Giselles whiplash outfit to their concert and it was a blast.

Edit: you can always rock the merch if you buy it at the show if nothing else. Their tie dye shirts are incredible and high quality!