I am guessing we can change the places of two different $\text {digits} $ in $n $. If that is the case the answer is $n=1520$ where you can permute $1,5$. EDIT : Isn't $n=800$ an answer? We can change the first and second digits to obtain $m=080$. Or do we have to interchange non-zero digits?

Yes, it is right answer. You need to prove, that it is minimal

babu2001 wrote: EDIT : Isn't $n=800$ an answer? We can change the first and second digits to obtain $m=080$. Or do we have to interchange non-zero digits? We can`t set zero as first digit.