There is no built-in function in excel to check the value of the cell is a valid date. In order to do this you have to make your own function.
Follow the steps below.
1. Open the VBA Script Editor of your excel. Select Tools->Macro->Visual Basic Editor or Press Alt+F11 on the keyboard

2. The Visual Basic Editor window will appear, then Select Insert->Module on the menu.

3. Copy and Paste the script below.
Function IsDateValid(cell) As Boolean
If IsDate(cell) Then
IsDateValid = True
Else
IsDateValid = False
End If
End Function
4. Save the module. And thats it your done!
To use the created function IsDateValid, the figure
