Try playing along to the radio, or a playlist on shuffle.
You must already have something of a musician's ear, it shouldn't take you long to start anticipating the changes.
Until you get an ear for distinguishing major and minor chords (it becomes intuitive) use the 'cheat box' root, fifth, minor seventh, octave. Sounds fine over any chord 🙂
Also if you miss a note, just walk up/down chromatically to the right one. It's called Jazz. People will be in awe of your skills.