What is the subequations counter named?

I am using align as an example here. You just have to use setcounter before subequations environment to change the parent equation number. Using setcounter inside subequations environment will change the child equation/subequation number.

setcounter{equation}{parent_equation_number}
begin{subequations}
setcounter{equation}{child_equation_number}
begin{align}
<You equations go there>
end{align}
end{subequations}

Hope, this helped!