This can be amended via a posting type in General Postings called a TFR and will only be available if you have the same periods for your Practices.
You can sometimes amend via your Case screens and it should update the matter this will be the Branch normally (set up in System Matrix).
This should not be changed if any postings have been done on the file to the other Practice as it will cause imbalances and support will need to rectify them.
If you have imbalances please raise a new case online and reference the title of this article.