How to find the corrsponding expression after working with natural units $\hbar=c=1$?

Just put in factors of $c$ and $\hbar$ in such a way that the units make sense. There is always a unique way to do this -- unique in the sense that if you have two options, they're equivalent. For example, the natural-units equation $E=m$ can be made valid in SI as $E=mc^2$ or $E/c^2=m$, but these are equivalent equations.