Read Datasource Value, Send To Textbox In VB Script

I want to read a value from a datasource and send it to a textbox on an ASP page from the page's attached VB file. 

Both the textbox and datasource exist, but I don't know the proper commands to get the datasource value and then set the textbox value to it.

 

Dim Text As TextBox = FormView0.FindControl("Header")

Dim SQL As String = "Select [Customer] From [Datasource]"

Datasource.SelectCommand = SQL

 

Oh yeah, I don't want the textbox control to be databound as shown: 

Text='<%# Eval("Customer") %>'