Let’s say you create a data validation on a cell, allowing only whole numbers from 1 to 10.

To know how to do that, see Allow only whole numbers from 1 to 10 in selected cells using Data Validation

When any user enters either a decimal number, or any other number apart from 1 to 10, Excel throws an error like this.

Now you want to customize the Title (Microsoft Excel) and the Text written in the Error message.

Let’s say you want the Title as “Only Whole Numbers”
and the Error message to be “Invalid entry. Enter only whole numbers between 1 to 10”.

Go to Data Tab, and click on Data Validation.

Then click on Error Alert, and type and Title and Error Message.

When the user enters an invalid entry, this will come up.