If your apprentice did not receive an invite there are 2 ways to send out another invite or reminder.
Go to the Apprentices tab and click on the specific apprentice.
You'll see in a orange box at the top of their dashboard this:
You can either select:
Send reminder: Send another invite email to the apprentice. An Invitation Sent text will appear afterwards stating the invite email has been re-sent.
Copy invite: Copy the link of the invite, which you then can use to paste the invite link into an email to send to the apprentice directly.