Are you sure you’re using the latest version of the Debt Planner template, @Delaney? I might have extended the lookup to accommodate more accounts in the past month or so. Use the Tiller Money Labs add-on to check the version of your template and update as needed.
I just checked and the latest version should allow you to look up from several hundred accounts, though only 25 can be monitored in the template. To see the full list of available accounts, you may have to unhide the rows at bottom AND the columns at right.