If there is any change in partnership or in your case, addition of a new partner in an already existing partnership, the following steps are suppossed to be followed by the Partners.
The Partners are then bound to inform the Registrar of Firms about such changes in the Partnership Firm. Consequent to which they need to draft a new Partnership Deed as per the changes and must again file the application along with required documents to the Registrar of Firms with the applicable fees mentioned.
Under section 63 (1), when any change happens in the constitution of the firm, if a registered firm is dissolved, any person who was a partner immediately before the dissolution or the agent of any such partner or person specially authorized on his behalf, may give notice of such a change to the Registrar of firms, specifying the date thereof.
Under Section 63(2), when a minor who has been admitted to the various benefits of partnership attains the age of majority and elects to be or not to be a partner in the firm, he or his appointed agent (specially authorized) in this regard, may give notice to the Registrar of firms that he has or has not become a partner in the firm.