To report a change in your circumstances online to Southend Council, you can use the Citizen Access Benefits portal. This will allow you to inform the council about any changes that might affect your Housing Benefit or Council Tax Reduction.
You can access the portal through the following link: report changes online.
Make sure to provide full details of the change and the date it occurred. If you can't give all the information right away, it's still important to submit your change as soon as possible to prevent issues with overpayments or underpayments.