What's the best way to let a company know their emails accidentally contain sensitive info?

A bit of a weird one this and I don't know where best to ask...

Pizza Express have sent me one of their marketing emails, but the wally mastering said email has flubbed the unsubscribe link, so I get to see his username, the file location on his Mac, Dropbox info, amongst other other things.

Their customer support appear to not care.

What's the best way to let corporations like this know "*Hey, one of your staff has naused up …

ask cybersecurity don email emails express file info link marketing pizza sensitive username weird