Pence had to break the news to Trump that he doesn't have that type of power.
Donald Trump has been doing everything possible to block the vote. He's made every call possible and is coming down to the last resort which would be dragging Pence under the bus. Vice President Pence is expected to certify the votes shortly but apparently, in Trump's latest attempt to overturn the election results, he's asked the VP to refuse to do so.
Trump put Pence in the hot seat, publicly. "If Vice President @Mike_Pence comes through for us, we will win the Presidency. Many States want to decertify the mistake they made in certifying incorrect & even fraudulent numbers in a process NOT approved by their State Legislatures (which is must be). Mike can send it back!"
The unfortunate part of this all, at least for the VP, is that he was informed that he doesn't have the authority to carry out such an act. And, he was the one who had to inform Trump of this at the end of the day, even as the president threatened that if he didn't help overturn the election, it would be politically "damaging."
"The New York Times report regarding comments Vice President Pence supposedly made to me today is fake news. He never said that. The Vice President and I are in total agreement that the Vice President has the power to act," Trump said in a statement after the NYT's initial report was published.
There's speculation that Trump might "lash out" but we'll have to see if that actually occurs.