How to convert a vintage car stereo to Bluetooth for classic cars

this is the link to the Bluetooth unit I used= Wang shufang WSF-SPEAKER, 1pc 2 * 50W Bluetooth 5.0 Digital Audio Power Amp HiFi Stereo Dual Channel Class D Amplifier Board For Speakers 30W~200W https://amzn.eu/d/fjVSKcS