combobox to textbox c# sapb1

I woud like to when i selected a value in combobox allow m populate certain text boxes such as, textBox1, textBox2 , how can i do that? it's an addon.

I'm creating an addon, and this time im working with form similar to bp, and payment run, So can get the information on my combo boxes, bur for example in sucursal its the defualt value, i would like to get the value from the combobox "cuenta" in the same time fill bic/swift code textbox and control no.... that's all