If, after making a successful submission, you need to make changes and file an amended return. Please see the video tutorial for a walk through of the process.
Alternatively, please follow these written steps:
Successful response from HMRC at Date Time
The process will run the same as when you filed your original return.
You can currently file up to nine amended returns online but all amendments must be made within one year of the submissions deadline. This means that for the 2018–19 tax return, amendments must be made by 31 January 2021.
You can find further information in our knowledge base article What's the deadline for my self-assessment tax return?
Note: HMRC will not accept amended returns online for the 2017–18 tax year and any prior years. If you need to amend returns for these years, you will have to send a paper copy with a covering letter.