If you mean for the entire world, I don't think you can, since the world generation in Minecraft is based on RNG.

Whenever the game has to generate a new world, it calls upon an algorithm known as Perlin noise. This algorithm outputs a pseudo-random value that is then used to determine the characteristics and features of the world. However, the algorithm always outputs the same value each time for a constant starting point (the seed). Thus, the same seed generates the same terrain every time.

Moreover, you don't generate the entire world at spawn time.
Chunks generate around players when they first enter the world. As they wander around the world, new chunks generate as needed.

The only way to "choose" biomes, I think, is finding a world you like, obtain its seed (maybe using some online database or a seed picker) and upload that world on your realm.

_{Source: Seed and Chunk.}

If you mean for the entire world, I don't think you can, since the world generation in Minecraft is based on RNG.

Whenever the game has to generate a new world, it calls upon an algorithm known as Perlin noise. This algorithm outputs a pseudo-random value that is then used to determine the characteristics and features of the world. However, the algorithm always outputs the same value each time for a constant starting point (the seed). Thus, the same seed generates the same terrain every time.

Moreover, you don't generate the entire world at spawn time.
Chunks generate around players when they first enter the world. As they wander around the world, new chunks generate as needed.

The only way to "choose" biomes, I think, is finding a world you like, obtain its seed (maybe using some online database or a seed picker) and upload that world on your realm.

_{Source: Seed and Chunk.}