Could you tell me how to use plain flour in self-rising flour recipes?

Self raising flour has baking powder or bicarbonate of soda added to it. These 2 are raising agents.
You can add one of these to plain flour and sift it together.

You can try this proportion of 1/2 tsp. of baking powder to 100grams of flour. Baking soda would require some kind of acidic ingredient in the recipe to make it more effective

Could you tell me how to use plain flour in self-rising flour recipes?

For each cup of all purpose flour add 1 1/2 tsp baking powder, and 1/2 tsp salt.;)