Hi Travis H1.
Thank you for posting your concern here at the Microsoft Community Forum.
We understand that you need assistance with accessing Microsoft To-Do using your new Microsoft account. Let us provide some tips that can help you access it with no issues.
There are some instances where your browser may return to the same page of your account. This may happen as your browser remembers your log in credentials or may return to cached page of your account.
Clearing your browser's cache and history can help you resolve this. It will clear the browser's cache which may be the result of returning to the same old page of your account. If the steps provided doesn't work, try using a private or incognito browser to see if the issue persists.
Should you need additional assistance, you can always let us know by responding to this thread.