It’s known as “Chorus” effect. Audacity does not have a built-in Chorus effect, but you can try
Blue Cat's Chorus - Smooth Chorus Effect (AU, VST, VST3, AAX Plug-in) (Freeware) which is a VST effect or Chorus Effect which is a Nyquist effect.
See Missing features - Audacity Support for how to install Nyquist plug-ins.
See Audacity Manual for how to install VST plug-ins.
It makes it much harder to help you if you don’t say what operating system you have or what version of Audacity you are using. You can’t use VST’s in Audacity on Linux.
Gale