There are a number of options out there. Here is a link from a while back for the same question…
Hope you find an app to meet your needs.
there are many personal training app out there for PT’s to use but the best i have used so far has to be trainerize. This App is unfortunately not free but if you incorporate the App with in your business model you can for sure cover the monthly cost and grow your business. This App can really improve your productively , time management and make things a lot easier to organize. my clients love it and i’m sure your clients will to.
Wishing you all the health and wealth