However, I need to give you an important heads-up first: (released in 2016). Using such an old version poses potential security risks and lacks many bug fixes. The current version is 3.6+ and includes built-in MP3 export support (no separate LAME download needed for most modern versions).
I understand you're looking for guidance on using the with Audacity 2.1.2 . lame-enc.dll audacity 2.1.2 download