If you double click the .mpr file the right modeler version will open if that version is still available on your system. If the modeler version can not be found you get a popup to select in which version you want to open your model.

If you already did open your 10.20.0 modeler you can open a local model. If that is an older version it will ask you if you want to migrate the model to that version. When migrating from Mx 9 to Mx10 it is a best practise to always migrate to a latest Mx9 and do the migration to Mx10 from that version.

Hope this helps, otherwise elaborate on what error you get and what steps you already did.

Regards,

Ronald