How to reprogram Arduino if USB port is already in use?
https://digistump.com/wiki/digispark/tutorials/connectingpro
It is suggested that in order to upload using the Arduino IDE you must:


Add the repository http://digistump.com/package_digistump_index.json in Preferences > Additional Boards Manager URLs
Install Digistump from the boards manager.
select the DigiSpark in Tools > Boards.
Then this is perhaps the important bit "You do not need to plug in your Digispark Pro before invoking upload"   So hit upload before connecting the Digispark.
Then connect the Digispark when prompted by the Arduino IDE.