Use values in a subform

Use values in a subform

HI

I have one form, with subforms.

In the form I have a Lookup field.

In the subforms I also have a lookup field with the same values of the field of the parent form.

How can I do that if I choose a value from the parent, when I add a new register on the subform the lookup field take the same value choosed on the lookup field from the parent form.?