Buddha had many teachers who taught him meditation. However he saw through purifying his mind that the meditation taught by his teacher would not free him from the rounds of rebirth. He practiced austerities and found that starving the body would not free him from rebirth, he found the Jhanas would not free him from rebirth. he almost died from not eating and a little girl found him and brought Buddha food until he regained his strength. Buddha made a vow he would sit beneath the Bodhi Tree until he finally broke the chains of suffering. That is when he discovered that taking insight (vipassana) meditation coupled with the Jhanas completely freed him...

There was no teachers to appoint him a Buddha because he found what had been lost for a long time...A Samma Sambuddha

A Samma Sambuddha, or Universal Buddha, is the highest level of Buddhahood. He attains Enlightenment, by his own efforts, at a time when the teaching is not known in the world. He has the greatest and most extensive powers, teaches the Dhamma and goes on to establish a Buddha Sasana or Community.

https://www.thebuddhistsociety.org/page/the-buddha