If you’re talking about the Blue Ringed octopus, then the treatment is to get put on a ventilator until the venom leaves your system. Symptoms are pretty noticeable, and respiratory depression is what kills you.

As long as you’re at a hospital in time, approx 30 min, they would start treating those symptoms regardless of knowledge of the source , taking the guesswork away.

Just to respond to your earlier statement. Novichok is very deadly, and does kill people most of the time. There is no cure, only treatment, and it does cause long term damage for many people who survive. If you’re wondering why the Russians use it, it’s because it’s easy to administer to someone, and it’s distinctly Russian, meaning they can use it as a political tool, to spread fear.