The function of a Protem Speaker is to

The Speaker Pro Tem (or Pro Tempore) is a temporary office appointed by the President (or Governor in states) to manage the initial proceedings of a newly elected House. According to constitutional practice and conventions, the primary duty of the Pro Tem Speaker is to preside over the first sitting of the newly elected Lok Sabha and administer the oath or affirmation to the newly elected members [2]. Additionally, the Pro Tem Speaker enables the House to elect a regular Speaker [3]. Once the permanent Speaker is elected, the office of the Pro Tem Speaker ceases to exist [2]. While the Pro Tem Speaker holds all the powers of a regular Speaker during their short tenure, their specific functional mandate is to swear in members and hold charge until the regular Speaker is elected, distinguishing them from the Deputy Speaker or a panel of chairmen who handle routine absences [3].

Sources

1. [1] Laxmikanth, M. Indian Polity. 7th ed., McGraw Hill. > Chapter 23: Parliament > Speaker Pro Tem > p. 233
2. [2] Indian Polity, M. Laxmikanth(7th ed.) > Chapter 23: Parliament > Speaker Pro Tem > p. 233
3. [3] https://www.mpa.gov.in/sites/default/files/parlia2.pdf