5个文本框，2个按钮。如何将textBox分配给Button？

I want to give my users the option to use a textbox and press Enter. The challenge is that I have 5 textbox, and 2 options. 3 textbox belong to one button, and 2 textbox to the other. How do I trigger a particular Button according to the textbox the user was in when he press Enter?I want to give my users the option to use a tex