"But as everyone else has said, and I agree with them, there is a time for reflection and then there's a time to get up off the canvas and rebuild."
Muller and former National MP Nikki Kaye rolled Simon Bridges and Paula Bennett from the party's leadership in a coup in May after polls showed support had plummeted after lockdown.
But Muller stood down after 53 days in the position because the role had a negative impact on his health and Judith Collins was then made leader.
Numerous MPs and commentators have included the quick succession of leaders among the reasons for the election result.
Muller said he would do things differently if given the chance but now was the time for reflection.
He also had "very strong support" for Collins and deputy leader Gerry Brownlee.
After standing down as leader, Muller didn't return to Parliament and first returned last week after the election.
Muller's message for National and its supporters was that they were only there "because of the efforts of them".
"And the relevance we have in New Zealand today. We need to earn every vote back day by day, week by week and we need to bring the best of ourselves to do that."