If the original welcome email link has expired here is how you can get everyone learning.
This article is for Training Managers
If you need to resend a welcome email, you can do this via the "bulk upload" tool on the users tab.
Ensure you have all the users you would like to get the email on the CSV file. All of the users on the list will receive the email.
Upload the file, and ensure you have the "Send welcome email - existing users" toggle switched on. 
As soon as you press continue, that email will be sent out to your users.