How to change the admin and add a new member (once the admin left the company)

[k.morkisz]

We are not able to add members due to the fact that the person who left the company was the admin.

[Philipp Sendek]

Hey Grant,

Zephyr for JIRA is quite powerful in terms of organizing, planning and running test cases; also it's available on JIRA Cloud which is a mandatory requirement if you're using a JIRA Cloud instance.
You can find the product info here: https://marketplace.atlassian.com/plugins/com.thed.zephyr.je#cloud 

Depending on the kind of application your QA team is testing, JIRA Capture could also be quite interesting for you:
https://de.atlassian.com/software/jira/capture

As for Zephyr, they also have several demonstration videos on YouTube that will help you get a good impression on how it works and looks.

I hope these fit your needs.

Regards,
Philipp