if condition in data validation - when false allow to type

I want to create a data validation list, with if condition.

When the condition meets true it should show the list and if false then it should allow to enter value manually.

How to do this.

Thanks in advance

Hi - can you attach a sample of your file?

Use a DV type of List, and a formula such as

=IF(A1="x",myList, "")

Thanks for your reply,
=IF(A1="x",myList, "")
this formula will give a blank space when condition meets FALSE, and wont allow to enter any value manually
I want to enter something manually when condition meets FALSE.

thanks in advance.