Once the Immunisation team has added you to the system, an automatic registration email will be sent to your account. Please, check your spam/junk folder or do a search in your email looking for "RIVIAM".
Also, check with your IT team that the firstname.lastname@example.org has been whitelisted.
You will need this email to activate your account.
If for any reason you still can't find this invitation email, please check with your Immunisation team if they have added you with the correct credentials.