How do i get a wet bicarbonate of soda stain out of my carpet?
You don't.

Maybe.

You might get lucky but sometimes a series of chemical processes ends up fixing the stain permanently. A research chemist and a lot of time and money might fix it but sometimes you have to consider alternatives.

Not too long ago, a plumber left a stain on a carpet. I went through a variety of products and services to try an remove it. In the end it was worse than it was before I started.

I paid a carpet fitter to replace the carpet.