Set a variable in data base with AngularFire

Hi, i try to change the value of a variable in a firebase data base.
But my code don’t work

this.afAuth.authState.subscribe(data => { // ajoute des tacoPoint 
      var ar = 0;
      let ab;
      const a = this.afDatabase.object(`TacoPoint/${data.uid}`)
     this.test = a.valueChanges();

     this.test.forEach(e =>{
      e.Tacopoint = e.Tacopoint + 20
      ar = e.Tacopoint;
    a.set({Tacopoint : ar})
    console.log(ar) //  0 in console 

The forEach loop is excute after the set() functions so i don’t know how to change that.
(sorry for bad Enlgish)
Thanks :slight_smile: