On your team page you can invite & manage users within your Junip organization: https://admin.juniphq.com/settings/team
To invite a new user, input their email & hit "invite user". This will prompt them to join your organization in Junip. Users must be invited by the owner, they can't just join the organization through the typical sign-up flow.
If you're the account owner you can also transfer ownership or remove any existing user in your organization.