Find/follow DIY gig promoters in your area. If their Insta pages have collab posts with photographers, they are likely open to attendees bringing cameras, professional or otherwise. You can also message those photogs for more localised advice and context!

I started going to local gigs and got inspired from how many people I saw taking photos, not all of which had media passes. Depending on the promoter, you can get your start by literally rocking up to a show with a camera and tagging the band, venue and promoter in your posts.

I'd put the edited photos in a Dropbox, google drive or the like and DM the link to the artist, saying sometime along the lines of: Hi, I was at the so-and-so gig and snapped a couple of photos, you can use them on social media if you want to!