licensing – Asking for permission to contribute in a proprietary software? What should i do?

First of all i would like to say that i love open source software. It’s free and a wealth of new knowledge of the things happening behind the curtain.
Now lets talk about the elephant in the room here, its been a few months since i have been using Termux ( Linux Terminal Emulator for Android (without root) ) for development purposes and testing purposes of software code when i am outside and not near my laptop etc. Its works better than other software that are very focused towards one language or other na├»ve educational programs by giving a lot of freedom to download and setup any software ( ofc not all ) But its not at all perfect as long as you’re unrooted butyesterday i saw someone use Pydroid 3 (another educational application) that has ported scipy, numpy and ML-related libraries to create a face detection app, Its an amazing app but and i would like to contribute to it or just look through the source. Reverse engineering is not an option so How should i go about it? What do i say if i ask for source code in email? What legal processes do i have to go through?