Debug/ Complete my existing iOS app

I have an existing XCode project that has:

- login/ signup functionality using our REST API
- allows user to pay for our products
- allows user to manage orders (free) and/or manage paid orders

I need someone with good iOS experience to:

- review/ test and complete functionality on Xcode
- modifies design elements (we can provide some design elements)
- guides me through approval process (incl. payments)

Thanks!