In order to transcribe audio from cassette tapes, you need to first convert the audio into one of the audio file formats we support, like MP3 or WAV among others.
To do this, you need a cassette to MP3 converter device, like one of the devices here: https://www.amazon.com/cassette-mp3-converter/s?k=cassette+to+mp3+converter
Once you have the MP3 file(s) saved to your computer, you can then follow the step-by-step instructions here to convert the audio into text: https://transcribe.wreally.com/how-to-transcribe-audio