Use the AfterUpdate event of the text box (or the Click event of the button
if you wish) to FindFirst in the RecordsetClone of the form. Test NoMatch,
and set the Bookmark of the form.
There's an example in this article:
Using a Combo Box to Find Records
at:
http://allenbrowne.com/ser-03.html
The article explains how to set up a combo box, but the code is exactly the
same for a text box.