Remove the radio. Check Youtube for removal. https://www.youtube.com/watch?v=gFvHl-MR6Io
Remove the metal covers. They are clipped on so just need to pry a bit with screwdriver.
Find the vias in the picture to solder your LEFT and RIGHT (Green / YELLOW) Audio Jack connector wires to and ground wire ( White) .
Then burn a blank CD. I burnt an audio CD with a 6 second silent audio track recorded with Windows Sound Recorder and thumb over mic input.
Some players do not switch to headphones mode when you plug in the audio jack so I needed to turn off car first.
1. Insert the Blank CD
2. Turn OFF the CAR
3. Plug in your PLAYER ( If Car is ON my PHONE does not change to headphones )
4. Start CAR and Play away
Also: You could also drill a hole in the front plastic and put in a jack like this https://www.digikey.ca/product-detail/en/schurter-inc/4832.2300/486-3419-ND/1731055. Then use a 3.5mm audio cable.