The problem is there is no other habitable world within reach of current travel technology.
Habitable means there must be breathable air, tolerable temperature, water, food and raw materials.
The likelihood we will discover a habitable world and have the means to transport the people and materials there needed to set up a new cilvilisation is close to zero.
We will likely wipe ourselves out way before that becomes even a remote possibility.
And it's probably good that we will because we have ruined the Earth and we would ruin wherever we went to next.
The only possibility we have is if some friendly aliens visit the earth and are benevolent enough to offer us their already-developed technology to achieve it.