There are many platforms out there like CLUTCH, Goodfirms and many more like these from where you can hire professionals for android app development according to your needs and requirements. This process will take lots of time to find a reliable company so i would recommend you to get in touch with InvoZone Pvt. Ltd. I found them on Clutch platform, Here is a link to their CLUTCH profile They have the best team of professionals, who will develop your app from scratch to end.
Hope it helps!