//declare the method
+(void) goGameScene:(int)lvl;   //SceneManager.h
+(void)goGameScene:(int)lvl {   //SceneManager.m

//to call the method
#import "SceneManager.h"        //in the .h of class you call it from
[SceneManager goGameScene:lvl]; //in the .m of the class you call it from

I wanted to make a function / method and pass a var to it form another class.

xcode declare and call method with parameter

function

Objective C