If you have multiple accounts in Outlook, you can set one of them as the default. Every time you open Outlook, the default account will display first. Please follow the steps below for details:
Step 1: Click the "File" tab in the ribbon;
Step 2: Click "Account Settings" in the "Info" section, and select "Account Settings" from the drop-down list;
Step 3: Select the account you want to set as default, and click "Set as Default";
Step 4: Click "Close" at the bottom to close the window.