Firebase Ionic set user id on push

Ionic Framework ionic-v3
1

I have my app in ionic 2 working great apart from when a user logs into the app, they all have access to the same app. The goal of the app is for a user to save their diary. What i want to be able to do is allow a user to save their data to their acount.

text: “Save Trip”,
handler: data=> {
let newDepart: String = diary.diaryd;
let newAriv: String = diary.diarya;
let newCode: String = diary.diaryc;
let newCoun: String = diary.country;
let newCity: String = diary.city;

            if(data.diaryd != ''){
                newDepart = data.diaryd;
            }
            if(data.diaryd != ''){
                newAriv = data.diarya;
            }
            if(data.diaryd != ''){
                newCode = data.diaryc;
            }
            if(data.diaryd != ''){
                newCoun = data.food;
            }
            if(data.diaryd != ''){
                newCity = data.city;
            }
            
            
            
                this.diary.update(diary.$key,{
                    country: data.country,
                    city: data.city,
                    diaryd: data.diaryd,
                    diarya: data.diarya,
                    diaryc: data.diaryc
            })

Any help would be great thanks in advance