By formants, I understand the following: region of amplified partial tones in voice sound spectrum. Or another definition: In acoustics, a formant is usually defined as a broad peak, or local maximum, in the spectrum.
My purpuse is to listen voice with changed formants.
I think that’s a bit too specialist for a general purpose audio tool like Audacity.
I’d suggest that you look at specialist voice analysis software, such as Praat.