$$ \mathcal{SO}_{2}(\mathbb{F}_q) \underset{\text{isom}}\sim \begin{cases} \mathbb{Z} / (q-1)\mathbb{Z} \hspace{0.2cm} \text{si} \hspace{0.2cm} -1\in \mathbb{F}_{q}^{*(2)} \\ \mathbb{Z} /(q+1)\mathbb{Z} \hspace{0.2cm} \text{si} \hspace{0.2cm} -1\notin \mathbb{F}_{q}^{*(2)} \end{cases} $$