If you ever run out of ideas for melodies, you can always break down your chords into single notes (arpeggio)
and play around with the spacing for a simple in-key melody/harmony. For a little more variation and originality, you can add any notes from the appropriate major/minor scale (according to what type of chord you just broke down) between the original notes from the arpeggio. Refrain from adding too many notes though, more notes could mean less space to play around with creative rhythm. If you have no clue what any of this means, come check out our music fundamentals course!