Does Audacity has autotune?

where and how to use autotune in audacity to improve the quality.

Autotune does not support Audacity.
For a list of apps supported by Autotune, see here on the Autotune website:

Other pitch-correction plug-ins are available,
some are free, e.g. …

There are some free alternatives available that sound quite similar.

Just search for “free auto tune plugins” or something like this on google.