score:1

try updating the state when fetching values from firebase:

return firebase.database().ref('users/trainers/').on('value', (snapshot) => {
    const childtrainersnapshot = snapshot.map(childsnapshot => {
        return childfirstname + ' ' + childlastname + ' ' + childemail
    });
    this.setstate({ childtrainers: childtrainersnapshot });
})

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