Adjust the plan date if busy

Hi everybody,
In my local excel forum has a query:
They do planning for the task, for instance, Task 1, plan date: 15-Mar. Now, they review and findout that they are busy that day, and may be some next days.
How to assign the new plan date to closest date that is not busy.
See attachment.
I've built my solution already, but it so complicated and i am not sure it is the best!