Write the next sentence in the following story.

How to complete a self assessment tax return
Register this year if you didn't send in a tax return last year.
You may already be registered if you turned in a tax return last year. However, if you did not send in a self-assessment form last year, you'll need to register again this year.
Alternatively, if you have registered in the past and sent in a return last year, find the unique taxpayer reference (utr) number that was sent to you. You'll use this number when filing online.