If you've mistakenly selected 'Agree with Demand' instead of 'Disagree' on the e-filing income tax website, it's not directly reversible. However, you can resolve this by submitting a grievance to the CPC and AO. Be sure to clearly explain the situation and provide supporting documents, as this often leads to an online resolution.
27 June 2020
You can submit a grievance to CPC & AO explaining the fact.
And upload the supporting documents.
Mostly your issue will be resolved online.
You may get mails for the resolution of the issue