PLUGIN KNOWKOUT

I not know whu instalation. AUDACITY 3.0.5 WINDOWS 10

Do you mean “Kn0ck0ut” (the vocal extraction VST plug-in)?

If so, that plug-in is obsolete and the official website is closed (http://www.freewebs.com/st3pan0va/)

Try using Audacity’s “Vocal Reduction and Isolation” effect instead: https://manual.audacityteam.org/man/vocal_reduction_and_isolation.html