If no candidate is determined to have a majority, then the contingent election procedure described in the Twelfth Amendment would be used. The House, voting by states, would elect the president, and the Senate would elect the vice president.
When thee is Failure to complete process
By imposing strict limits on procedures, debate, and recesses, the Electoral Count Act is designed to help Congress achieve an election result before the term of the outgoing president ends. Nevertheless, if no new president (or vice president) has been elected by that time, the Twentieth Amendment and the Presidential Succession Act would mean that the Speaker of the House would be sworn in as acting president.
https://en.wikipedia.org/wiki/Electoral_Count_Act