Carefully review the Editor Tutorial inside the app in Settings/Tutorial
(You can also select the "?" in a circle at the top of an app page)

Place the cursor in the correct space
Tap the pencil icon that's beside the chord input field
Select the root
On the next page, select the quality
On the next page you can select the bass-note (slash-chord) if any
When done, touch the check-mark ✔️
)BOB