Tax on regular assessment is the tax that a taxpayer is required to pay against a notice of demand from the Income-tax department. So when a notice of demand is received and it is found that some additional tax is required to be paid, the same shall be deposited under the head "Tax on Regular Assessment".
The steps for making payment of Regular Assessment Tax will be same as that of Self Assessment Tax. The only difference is that in the field of "Type of payment", you will have to select " (400) Tax on Regular Assessment ".
To know how to pay Self Assessment Tax online, click here