You can update your tax return by following these steps:

  1. Log in to your HMRC Self Assessment account

  2. Click ‘More Self Assessment details’

  3. Click ‘At a glance’

  4. Click ‘tax return options’

  5. Choose the relevant return

  6. Make the corrections in the return, and file it again

In case of Paper Tax Returns, download a new tax return, and send HMRC the corrected pages.