Hi Ali,
If you have a government gateway user ID and password, you will be able to submit your return online from India.
You can also contact HMRC at
Self Assessment: general enquiries to obtain your UTR.
Can you also complete form P85, to let HMRC know you are leaving the UK.
The form can be found at
Get your Income Tax right if you're leaving the UK.
Can I also ask that you review the guidance on residence and complete the tests at RDR3, so that you can determine your residence position for this tax year.
RDR3 Statutory Residence Test.
Thank you.