modify mobile app

I am looking for a skilled mobile app developer to modify my existing app. The app is currently available on both iOS and Android platforms. The modifications required are adding new features to the app. The new features have already been planned out and I am looking for someone who can efficiently implement them. The ideal candidate should have experience in mobile app development, particularly in adding new features to existing apps. The skills required for the job include proficiency in both iOS and Android development, knowledge of mobile app design principles, and experience with app performance optimization.

the existing app will be sent in a chat box
the budget is $300-$350