You can wash it out (likely to an extent) with clean water.
Use a syringe/pipette to put water up there. Don't breathe the water in, obviously.
You'll be flushing your sinuses out.
If the burning doesn't go away then I suggest stopping and going to A&E.
You should feel very very silly for putting baking powder up your nose.
It was a replacement for coke.
Whether you mean Cocaine or not, and you actually take Cocaine or not, you should not snort or put things up your nose at all, especially powders.
They can kill you or do serious damage.