Leavening Agent

as a substitute for 'self raising flour' use flour and a leavening agent…

specifically substituting spelt

To substitute white spelt flour for self-raising wheat flour, convert your wheat recipe by either reducing liquid ingredients in your recipe by 10–15% or increasing flour quantity by 10–15% then sift in ¾ teaspoon of baking powder with each cup of white spelt flour.

see also https://www.wikihow.com/Substitute-Spelt-Flour-for-All%E2%80%90Purpose-Flour