You want one control to specify the settings of another; that's called a master-detail relationship. I googled a number of different options for drop down master controls.
Just a side comment, but I would recommend using textboxes with care in your case. If you use a textbox, it's usually to allow someone to enter or edit a string however they want. In most master-detail relationships, you probably don't want people to have that level of control. Usually, the master control lets you determine what output someone will see, or what functions they have access to, or what subset of data they want.
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