Ionic viewchild(nav) push not function

hi in app.component im using

@ViewChild(Nav) nav: Nav;

and for go to another page im using

this.nav.push(PrivacyPage);

but when i want use viewchild in another page not working and show error
"push not function"

when i using navcontroller swipe back not working :cry:
but when i using viewchild swipe back working :heart_eyes: