QuickBooks Self-Employed (QBSE) does not support multiple user logins, Sophie.
If you need to provide access to your assistant, you can either share your login credentials or consider upgrading your QuickBooks subscription.
For future reference, if you want to modify your Intuit credentials, you can visit this article for guidance: Update or change your Intuit Account sign-in information.
Feel free to leave a comment below if you have any other QuickBooks-related concerns. We are always available to assist you.