This is one a few recent lessons I've done on ear training for bass players. It's an area I highly recommend you work on daily because, if you're good at this, you can teach yourself so much.
You become your own teacher by figuring music out by ear. It's a skill that can be acquired like any other.
You'll find the other lessons on this site or on this YouTube Ear Training For Bass Players playlist (can you do me a favour and subscribe to my channel once you're there? Thanks!).
Work Out Movie Themes By Ear
In the video lesson above, I show you how to take a simple set of notes (either a major, minor, or lydian mode) and find the melody by ear using those notes. It takes a little repetition (what doesn't??) but after a while you will find yourself being able to do this easily.
Pick easy themes (or songs or bass lines) and aim to play it on your bass. Here are the themes from the lesson.
Superman On Bass
Jaws On Bass
Close Encounters Of The Third Kind On Bass
Indiana Jones On Bass
Star Wars On Bass
The Simpsons On Bass
Back To The Future On Bass
Go through the videos above (or wherever you listen to audio) and take small sections of a melody. You'll need to press the pause and rewind buttons a lot and exercise a little patience but stay with it, and you'll find similar patterns being used time and time again.
You'll then be well on your way to learning this musical superpower!
Write down the melodies you're learning in a practice journal and build a routine where you do a little bit as regularly as you can.