Doesn't do much. Your best bet is to lead people to alternatives, and thats assuming they care enough to do so long term. Boycotts might kill little companies, but something like H&M requiresI'll never forget in TLR all that "we gonna boycott unilever for its racist ads" talk but that never materialized.
I went as far as saying "Hey I'll throw away my big can of Lipton Tea down the toilet and make a video and we all do the same and hopefully we can go viral and make some noise" No one in TLR budged.
catastrophic shyt in order to feel significant hurt. I'm sure blacks don't make up that much of their base, and any losses would be functionally inconsequential.