The first step is to head to Admin -> Company -> Company View to view your people. In the top right, click the dropdown next to "Add new person" and you should see the option to "Export to Excel". Click this to download a file containing all of the people in your system, along with the date on which it was exported.

Note that this file does not include people that are archived or have had their access revoked.

The file you just downloaded is compatible with each of Frankli's bulk upload workflows. The one you'll want to use to restore your people to how they are in the file is the option labelled "Update people from file". This option is also located inside the "Add Person" dropdown.

The rest of the restoration workflow is the same as a bulk update, which you can find more info about here.