when you add server validation to your page, a new binding group is added to the bindings panel named Validated Entries. This binding group contains a binding for each form element, and will contain the value of the form elements that passed validation when the validation fails.
In design view, select the first element, in the property inspector, click the lightning bolt icon next to initial value. from the bindings panel, expand the validated entries binding group and select the corresponding binding. rinse and repeat for each additional form element.