from tkinter import *

class MainWnd:
    def __init__(self,Frame): 
        self.SelectName = StringVar()
        self.Names = ["aa","bb"]
        self.OptModuleName = OptionMenu(app,self.SelectName,*self.Names,command=self.SelectModule)
        self.OptModuleName.pack()
        self.BtnUpdate = Button(app, text="Update",command=self.Update)
        self.BtnUpdate.pack()
    def SelectModule(self,value):
        print("choose",value)
    def Update(self):
        print("Update Obtion Menu")
        self.OptModuleName['menu'].delete(0,'end')
        self.Names.clear()
        self.Names = ["cc","dd"]
        for Item in self.Names:
            self.OptModuleName['menu'].add_command(label=Item,command=self.SelectModule)
app = Tk()
app.geometry('300x200')
MainWindows = MainWnd(app)
app.mainloop()