How do you do this? What if you are a beginner to chords? How do you know which chords match the song you wrote?
Determine what key the song is in, and play around with any chords that fit the same general warm tone of the song. Throw them in as replacement chords for some that you found to be too flat, or throw in some extra chords on the off beats without disrupting the general harmony and melody of the song.