Let $\mathbf{G}$ be a split connected reductive group scheme over a scheme $X$.
Let $X'\rightarrow X$ an étale Galois cover of group $\Gamma$.
We consider $G$ a quasi-split group scheme over $X$ that splits over $X'$ to $\mathbf{G}$.
How can we describe a $G$-torsor on $X$ in terms of $X'$ and $\mathbf{G}$?