1. Why did the leader ask you to give a new employee job training to the old employees?
2. What do the old employees think of your training?
3. What does the leader mean by your approval (is it to promote you or replace others)?
4. Learn more about whether there are intrigues or other superficial phenomena in the new organizational structure?
Now that the leader has spoken, you must do it. If you feel that there are indeed many unstable factors, you can simply share them in the group first and don't give you any more training.
As a newcomer, you should keep a low profile before you have a clear understanding of the organization. You can learn about your leadership and work style, and the thoughts of some people at your level at present, or learn about the atmosphere of the whole organization first.