How can you set the resolution in twitch streams exactly as you want (if you stream yourself)?

When I stream you can only choose the resolution I specified, how can you use multiple resolutions? So from 160p - 1080p and not just 1080p or something.

(use streamlabs)

So from 160p - 1080p and not just 1080p or something.

What you mean is transcoding.
But you can't hire. This feature is only available to Twitch partners and is automatic. But even a few random affiliate streamers will be assigned this function per stream if the server has enough capacity. It is possible that the function is there in a current stream, but not in the next stream. Unless you're a partner.