Extension of end dated task in Project

Hi All,

in one of our project it has been found that some project related expenses are not interfacing due to that project related task has been end dated. So am trying to extend the task completion date then am getting the following Caution message:  

Caution : If you change the start date or the completion date for a task you must baseline task level budgets associated with the project. Do you want to change the date?

What steps I have to perform in order to extend the Project Task completion date.

Regards