Hi Kain Shin,
Your tax return will still be processed.
If you do not need a business account you can try:
1. select the ‘Business tax account’ in the top Nav Bar on the landing page
2.select ‘Manage Account’ in the top Nav Bar
3.select ‘Stop access to a tax duty or scheme online’
4.select 'continue' on the screen showing the UTR being removed
5.select 'Remove access'
7.exit Business tax account and access Personal tax account.
If this does not work then you can contact out Online Helpdesk:
Technical support with HMRC online services