Welcome to the forum, @ChrisClayt. To get Dorico to recognise your MIDI files as being written for piano, there are a few things you can do.
The optimal solution would be for Dorico to recognise your MIDI files as containing music for piano automatically. It will do this if the track name in the MIDI file is “Piano” (or something similar), or if it uses MIDI program number 0 and you have the Use GM program changes to identify instruments option activated in the MIDI Import Options dialog.
Given that your MIDI files are coming from your digital piano directly, I don’t know whether or not you can easily influence the way the MIDI files it generates are set up – you would need to consult the documentation for the digital piano to find out.
The other way is simply to tell Dorico that the track in your MIDI file are for piano. When you open the MIDI file in either Dorico Elements or Dorico Pro, you’ll see the MIDI Import Options dialog, in which you can specify which instrument Dorico should use for each track in the MIDI file. Simply telling Dorico that the track in your MIDI file is for piano should be sufficient. (The MIDI Import Options dialog is not included in Dorico SE.)