Forms :: Send Data From Pop-up Form To Main Form (sub-sub Form)

On the form: User enters first name, then last name. Upon updating the last name field, I would like another form to pop-up and display all the people with that same first name and last name that the user just entered.

On the pop-up form: All of the matching first names/last names are listed with a button control beside each record that says 'Select'. The user clicks the select button beside the record he/she wants. This pop-up form closes and all of the data from this selected record is now showing on the original form.

So far, I have a query/form that pops up only showing the matching first/last names. I'm having a hard time getting my original form to auto-populate with that record that the user selects on the pop-up.

(Also my main form is actually a sub-sub form - so in my trials I could've been massacring my syntax trying to point to it.)