main.go

type User struct {
	ID           primitive.ObjectID `json:"id,omitempty" bson:"_id,omitempty"`
	FirstName    string             `json:"first_name" bson:"first_name" `
	LastName     string             `json:"last_name" bson:"last_name" `
	EmailAddress string             `json:"email_address" bson:"email_address" `
	Password     string             `json:"password" bson:"password" `
	CreatedAt    time.Time          `json:"created_at" bson:"created_at" `
	UpdatedAt    time.Time          `json:"updated_at" bson:"updated_at" `
}

// updateField 
func updateField(id string, key string, value string) error{
  objID, _ := primitive.ObjectIDFromHex(id)
	filter := bson.D{{"_id", objID}}
	// 1. with set only
	update := bson.D{{Key: "$set", Value: bson.M{key: value, "updated_at": time.Now()}}}
	// 2. with push only
	update2 := bson.D{{Key: "$push", Value: bson.M{key: value, "updated_at": time.Now()}}} 
	// 3. with push and set
	update3 := bson.D{
		{Key: "$set", Value: bson.M{key: value, "updated_at": time.Now()}},
		{Key: "$push", Value: bson.M{"created_at": time.Now()}}
	}
	
  
  _, err := client.Database("database_name").Collection("database_table").UpdateOne(
		context.Background(),
		filter,
		update,
	)
  if err != nil {
		return err
	}
}