Only verified users can take any action in Jira like creating and updating an issue. It is a one-step process and user get a login button in the Home tab of the bot channel or they get the prompt when they try taking any action on Jira.
The admin can send also reminders to all unverified users in one click. You can find this option under User Mapping.
You can also send the reminder individually as well using the reminder button available next to every unverified user.