To setup email forwarding:

Visit https://www.office.com/ and sign in using your Office365 credentials.
Select Outlook
Select the Cog symbol along the top, this will open up Settings
Click View all Outlook Settings (last option)
On the Email tab click Forwarding.
Tick the Enable Forwarding box and enter the forwarding email, click Save and your emails are forwarding.

To stop forwarding:

Visit https://www.office.com/ and sign in using your Office365 credentials.
Select Outlook
Select the Cog symbol along the top, this will open up Settings
Click View all Outlook Settings (last option)
On the Email tab click Forwarding.
Untick the Enable Forwarding box, click Save and your emails are no longer forwarding.