To get a UTR number you will need to register for HMRC online services. To get your UTR number you will need:
Date of birth
Address
National Insurance number
Your email address and contact number
The name address and nature of your business
Your business telephone number
The date your self-employment started
Once you have successfully registered HMRC will post your UTR number to you, if you need to access your UTR number sooner you may be able to do so through the HMRC app.