This ad on a YTMP3 converter makes it seem as if it's the button you are supposed to click to convert (sorry for bad quality. I'm working on a school project) :
YTmp3 MOD APK v4.6.1_ytmp3web (Unlocked) - Apkmody
YTMP3 YouTube To Mp3 Music Converter - Codeplayon, 52566370 - expatriates.com
15 Best YTMP3 Alternatives to Save YouTube Video to MP3