You will need hard evidence, documentation, irrefutable proof. This is why writing and texts are so sought after for cases like this. As for anonymity, good luck. I had to file a report once, it was blaringly obvious it was me despite refusing to give my name (they asked twice jUsT tO fUrThEr CoNtAcT iN cAsE). If you wanna do it, you need to get other people on board. Documentation, witnesses, the whole shebang. And they hardly ever do anything unless it's something hard, like theft or the most blaringly obvious harassment.

Something happened at my store. A barista reported them & the district manager contacted my manager directly & it was obvious who made the report. Although the barista was making far fetched claims, it was stupid how the anonymous tip line wasn’t anonymous at all. It went up the chain & right back down.