If its a CRUD menu, go to "Userview Builder > CRUD menu > Properties > UI (Edit) or UI (Add)".
Read at CRUD Menu#Add.
i'm don't have CRUD.
You can use Javascript/jQuery code to relabel buttons, set in "Userview Builder > Advance > Custom JavaScript":
$(function(){ $("#cancel").val("Close"); });
I google and found lots of JS examples in Joget's Javascript API.