I have a user form with a textbox and two command buttons. The command
buttons are named Add and Done. When the user hits add I want the text in
the textbox to be added to a variable array. When the user hits the done
button I want to find each value in the array in the first column of the
active worksheet and replace it with the minimum value from the array.

How do I create this array?

How do I pass the array to the done button click event?

Private Sub Add_Click()
Dim a() As Variant

ReDim Preserve a(UBound(a) + 1)
a(UBound(a)) = textbox1.Text

End Sub

This gives me a subscript out of range message.