1)

Add proper URL rules and select "Validation" from the tooltip types

2)

Select a validation type from here

Capture the element where you want to apply validation

3)

As we have shown the captured element as an email field, we will select "Email address format"

4)

Enter a message for the users to follow

Select a suitable position

Click "Save"

5)

Publish this tooltip and it's respective parent folders

6)

As soon as you will start typing something, a validation message will appear