Mix two audio tracks - stretch one to sync with other
I suggest you try Audacity, which has very powerful audio editing tools, including the duration stretch/compress and pitch change functions. I've used it many times for a variety of audio tasks over the past 10 years or so. I cannot recommend it more highly. Catalina is not currently supported, however.

If you need to save to .mp3 and other formats, you will need the FFmpeg library (links on download page) for these functions.