It's easy to think of harmony as just chords of notes, something that melodies and tunes just sit on top of. The reality is a bit more complicated -- melodies are closely related to their chords.
You can experiment with this relationship by turning simple chords into melodies, using the tool on this page.
So far, all three chords have turned into melodies that just go up step by step, but melodies can obviously be more interesting than that. If you click on Change tool bank, you can see all the available tools. Select the Shuffle time tool, then click on one of the groups of notes. This tool randomises the order of the notes in each group. Try clicking again on the same group to get a different ordering, until you have an interesting melody.
Try experimenting with the Shuffle time tool with all three of the original chord groups to see what kind of melody you can create.
Obviously making great melodies is more skilful than just randomising notes but this shows one way you can make melodies from chords. The important thing is that the three melodies are closely related to the original chords -- the melodies came from the chords, in this case.
You can improve your melody by using some of the other available tools, such as Move and Duration.