Computing an element that generates the quaternion ideal

Question

Let $B$ be a quaternion algebra over $\mathbb{Q}$, let $\mathcal{O} \subseteq B$ be a maximal order, and let $I$ be a left $\mathcal{O}$-ideal. I know that there is an element that generates $I$, i.e., $I=\mathcal{O}\alpha+\mathcal{O}\text{nrd}(I)$ since locally $\mathcal{O}$ is left principal ideal ring. How could I compute this element $\alpha$ (on Magma or Sage)?