To e-verify income tax return (ITR) using Aadhaar OTP, one has to select e-Verify Return option on the income tax portal, select the option to verify using OTP on mobile number registered with Aadhaar and click on continue. Select the option to agree to validate Aadhaar details and generate Aadhaar OTP. Click 'Validate' option after entering the 6-digit OTP.