Currently, the Content Scheduler only supports connections to Facebook Pages and Groups.
To resolve this, you have a couple of options:
Create a Business Page using your desired name or branding. Once created, you can connect Express to this Business Page and schedule your posts accordingly.
Alternatively, you can continue creating your posts as usual and manually upload them to your personal profile on Facebook.
These options should help you navigate the issue with the Content Scheduler. Read more on how to connect social media.