You can upload your TomTom workouts directly from TomTom MySports to Endomondo.com.
Connect your TomTom device to your computer -> launch TomTom MySports and click Settings
Click Upload & Export -> Click Add -> Select Endomondo from the list.
Your TomTom workouts will now be synchronized to your Endomondo profile everytime you upload a workout to your TomTom profile.
Please note that this is a one-way integration - Workouts tracked with Endomondo will not be pushed to TomTom MySports.