When migrating task flows, you will be presented with warnings about what will happen and recommendations on what to do.
For the task flow itself, you will see:
The target organization has an object with the same name. Change the name in the source or target organization to migrate this object.
For tasks within the task flow you will see:
The target organization has an object with the same name. If you continue, the object from the source organization will overwrite it
If you only need the tasks within the task flow updated, check the box when you are prompted as shown below:
If you need the task flow updated as well, delete it first. If you want to preserve it for rollback, rename it (as suggested by the warning message).
Scott S Nelson