I don’t know if you are still having this problem, but this is how I just resolved it:
1. add Charles Schwab to your investment accounts
2. go to the app’s homepage, and click on the profile button in the top right corner
3. Click on accounts.
4. Find TD Ameritrade and click on it anywhere in its box. The layout makes it look like this is just a list of your accounts… But they are actually buttons.
5. There should be a delete button there, and you can delete it now that you have added your Charles Schwab account
