An external issue is anything outside the organization's control that can affect, positively or negatively, its operations and/or results.
Considering that, the question about "how" is answered by identifying operations and/or measurable results that can be affected by Covid-pandemic. For example, a manual production line is an operation that can be affected by Covid-pandemic, and productivity and revenues are examples of the affected result.
The question about "if" is answered when you consider that a Covid-pandemic can have a significant impact on operations and/or results. For example, if in your region of operation there aren't many recorded cases, the impact is less relevant than if your region is under a lock-down.
This article will provide you a further explanation about external issues: