What is impulse response if i know input and output?
If $x[n]$ is non-zero for $n=0\ldots2$, and $y[n]$ is non-zero for $n=0\ldots3$, then $h[n]$ must have non-zero components for $n=0$ and $n=1$. This is a property of the convolution.

So now you have to solve $y[n] = h[0]x[n] + h[1]x[n-1]$ for the relevant values of $n$, and there you go.

Start with the edges ($n=0$ and $n=3$).