The imperative of the verb “πηγαίνω” (or “πάω”) in the second singular person is “πήγαινε” or “πάνε”.
“πήγαινε” is more formal, while “πάνε” is used mostly in oral informal speech.
The word “πάγαινε” that you might have heard somewhere is either used as an idiom instead of “πάνε” in some villages in Greece, or it is used as a swear word, when we are annoyed by someone. It sounds insulting and degrading.
Example: “Άντε πάγαινε από δω!” = Get lost!