The email invite you should have received will contain a Username and Password to enable you to sign-in to MTIS. Visit the MTIS Sign-in Page to use these details.
If you have not received an email inviting you to join an MTIS account from the Organisation Supervisor, contact them to request that they issue an invite to you through their MTIS account.
Please note that you DO NOT need to register for an MTIS account through the MTIS website if you are joining a pre-existing account. Your account must be initiated by the Organisation Supervisor through their MTIS account.