I only have self-rising flour. Do I just reverse the substitution for using all-purpose flour when self-rising is required? (By the way, when making turkey pot pie with
Bisquick, I discovered I didn't have any eggs. As instructed on your site I substituted mayonnaise for the eggs excellent!)
You're walking on pretty thin ice, mister (or ma'am, or missy, or Ms., or whatever). Just what ingredients do you have on hand that you have to substitute mayonnaise for eggs and self-rising flour for plain flour? Well, at least you're cooking, and in our eyes, that's a very good thing.
There are a lot of recipes that will turn out badly if you try to take the self-rising out of the flour and engineer your own version of plain flour. Baking tends to be fussier than other types of cooking, and precision with the ingredients and measurements can be very important to the successful outcome of a dish.
At the same time, if it's a fairly straightforward recipe and there's a teaspoon or so of baking powder or a quarter-teaspoon or so of baking soda per cup of flour, then you might be able to leave out the leavening and substitute self-rising flour for the all-purpose flour. You would also want to cut back on the salt in the recipe, again in the ratio of a teaspoon per cup of flour.
We're making no guarantees here. You're breaking some rules, and you know it. But, since we have no idea what you're making, we'll let you give it a try.