You can solve for the lift generated by each rotating blade. Then it's roughly the same calculating the lift for a fixed wing, except for the freestream flow sp

You can solve for the lift generated by each rotating blade. Then it's roughly the same calculating the lift for a fixed wing, except for the freestream flow speed varying along the span. The lift is different at each spanwise location, so you integrate to get the total lift for one blade, then multiply by the number of blades. Numerous ways to do this, but the simplest accurate way is via lifting-line theory. The resulting system of equations is solved iteratively.