Enable menu strip from another form

[C# Programming]

I'm a very new C# programmer. I have two form (frmMDI and frmLogIn) when running the project, frmMDI form starts firt with some menu items are disable. But when I click another enable menu then frmLogIn comes. My question is HOW DO I ENABLE MENU ITEMS ON FRMMDI FROM FRMLOGIN?

Thanks
Visoth