With Voiceflow's export for Nuance Mix, you will download a (.trsx.xml) copy of all your assistant's NLU model data. This file will include all intent, utterance, entity and entity value data.
In your Nuance Mix Dashboard, select a project you'd like to upload the data to, and then open the Import/Export tab on the right. Select the ".trsx, .xml, .zip" import option, and select your export in the file selector. This will overwrite all data on your project.
More information on the Nuance Mix import process can be found here.