Replacing text up to a specific character?

Question

Visual Basic

It is necessary that the replacement works only up to a certain place in the text, for example, up to the @ symbol

Dim filter As String
        filter = TextBox1.Text.Replace("A", "").Replace("a", "")

        TextBox2.Text = filter

Answer 1

Split
Substring
Something like this

Answer 2

Split the string into two parts.
Make a change in the first part.
Connect the lines back.