Hi ya just thought id share this app i come across via a YouTube video.
There is an app called TUNE IT YOURSELF. Most of these tuning apps aren't brilliant, but this one really seems to work on the 3 cars I have tried it on so far. Unlike most you connect it up to Forza 7 or horizon 4 and it reads your telemetry as you test drive and adjusts the tune based on it. You still have to test drive as you go as it doesn't just give you figures and that's it, it gives you adjustments to make to the tune as you go.
There is a free demo of it in the app to give it a try but its cheap Monthly subscription of £1.40 or £14.99 for a year.
Just thought Id share it with you guys I have been out the Forza loop for a few years till recently so apologies if this is old news.