Which model ezcap USB cassette converter?
Likely the cassette converter is using 1/8 " (3.5mm) audio plugs or ports - mono/stereo?
Make and model laptop?
What audio ports (if any) does the laptop have?
What earpiece? What does the plug end look like?
(Being able to hear music via the cassette is a good sign.)
Cassette < 3.5mm plug (Male) ? ----- audio cable -----> Ear piece.
Corrrect?
FYI:
https://www.cablechick.com.au/blog/understanding-trrs-and-audio-jacks/
The laptop's audio capabilities must allow you to configure the appropriate laptop port for audio input.
And you must have the correct physical connections (TS, TRS, TRRS) throughout the audio path as well.
Lastly, the laptop will need software to play and/or record the incoming audio.
One requirement might be some audio adapter going from 3.5 mm plug (Male) to USB.
With matching pinouts (TS, TRS, TRRS).
For example:
Cassette < 3.5mm plug (Male) ----- audio cable -----3.5 mm plug (Male) ---->USB adapter ====> Laptop USB port.
Feel free to edit and correct my diagrams as necessary.