Harmony plays a much less functional role in most electronic music. At times, a pad playing a sustained root note is enough to make a track feel “full,” or perhaps a sampled chord progression or drumbeat is all you need in addition to your melodic line.
Search through the sample packs on Bandlab and find some samples that you think will work well with your melodies. Add a simple harmony line with a synth pad sound. Begin automating your mix to create a shifting soundscape.