HELP G&G m416 charging handle spring fix

so i have a 416 it was blow back but the guy i got it from removed the g&g mechbox so its not blow back. what id like to do is attach a spring for the charging handle so its not just sliding free in the gun any ideas on how to do it? i know in normal aegs there's like a pin or bar in the front end of the upper where a spring is connected to that bar is not in the 416 upper. any help is appreciated if needed i can post pics.