You can only enter chords on the Scaler keyboard on the CHORD page and not on the MAIN page, or EDIT page. There are a number of tutorials covering various functions on the Chord page: These are
Introduction to the CHORDS page
Introduction to CHORD Variations
Adding Augmented Chords Tutorial
The Chord Page: Inversions
I think these tutorials will show you how to enter and modify chords on Scaler using the keyboard.
I don’t have an audio input, and do not use Studio One, but I think you may have to use the ScalerAudio vst to detect audio input. This video from @davide covers the workflow for audio detection.