You should look for a degree in software engineering, mobile application development, mobile computing, computer science or a similar programming-centric field of study. Mobile software developers use coding languages such as Java, Objective-C, HTML5 and more to bring apps to life.
Before choosing a professional, you may also want to ask for examples of past work, which could include trying out some of the apps they have worked on. You could also look at their profile page on Bark, and Bark can show you reviews from past customers too, as well as examples of work that they have completed. This might also help you get some ideas for the kind of apps you might like and the level of complexity needed.