Go to https://webmail.htop.org

Click on the Outlook icon

Wait for outlook to load then click on the User icon in the top right corner

Choose 'Open Another Mailbox'

Type in the name of the mailbox to add rules to and select it

Click the gear icon in the top right

click 'View All Outlook Settings' at the end of the settings dialog

Click Mail->Rules

Click 'Add a rule'