Jazz Improvisation is Spontaneous Composition. Here’s a Lesson in How to Create Melodies

How can I start creating melody that goes with my chord progression?

Without knowing your level of musical ability, I think that no matter what level you are, you can safely start with either or both of these two different approaches:

1. The other way would be to play the progression using different inversions of the chords as you make smooth stepwise motion in your chord progression. Once you come up with some nice smooth and melodic connections of the chords the melodies will begin to be obvious to you immediately. You probably won’t hear the melody “all at once” but you will hear the basic skeleton and then the more you work with it you can then start to hear how to embellish it and come up with an interesting melody. Don’t think about the theory of what are the correct notes of each chord, just let your ear guide you and try to let it happen organically. The more you work with the progression the easier it will get to hear the notes that work naturally over the chords.

2. Set some kind of rhythmic feel with the progression that you may already have in your head, and lay that down on a recorder or garageband. After you have a basic feel or groove laid down, you should then play it over and over and start to listen in your head for melodies that come naturally from the progression. Do this over and over and eventually you may even be able to hear the progression even without the recording. Then you really hear the whole thing and see if you can hear a melody. Or you can just start to sing little melodies that you come up with and record them as your experimenting. The more you get the progression in your head the easier you will start to hear an organic melody, rather than just trying to peck something out on the piano or other instrument, it will usually get in the way as you stumble trying to find the notes. Instead, try letting your creative mind work without being distracted by the technique of the instrument. Using your voice in conjunction with your ear is always the most natural and musical way to create music.
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There’s plenty of other ways to create melodies as well but in general, using your imagination rather than trying to try to play it on an instrument, even if you’re proficient on the instrument, it will tend to get in the way. Your voice does not get in the way (except if you have absolutely no concept of pitch) and by using your voice you are in more direct connection with your creative mind.