To link to new records in a current account, the doctor's office will first need to invite you to access your records. This will generate an email invitation which will allow you to set up the account. Then, choose to “Link to an existing Patient Fusion account” after verifying your identity during registration.
At this time, through this process there is no way to link records for two accounts that you already have access to. If you would like to link two existing accounts, you can ask the doctor to revoke your existing records access and then provide you with access again. You can then link the records to an existing account when registering, as shown above.
For more information, please see How can I view multiple records that I've linked into one account?