If it has already happened

Move quickly and without shame. Contact your bank immediately — some transfers can be stopped or recovered within hours and almost none after weeks. Report it to the national fraud body, tell your institution, and change any password you gave away along with anywhere you reused it.

Then tell people. The reason these approaches keep working is that almost nobody says it happened to them, so every new person meets it fresh. Saying it plainly in a group chat is genuinely more useful than any warning poster.