Well done! I've been running on the treadmill all winter as it's been so wet, I haven't been able to get out (off road too boggy, and roads that I usually run on have been blocked by floods). It does get easier, my tip is to really think about your breathing, and breathe in time to your stride (so maybe 3 strides to breathe in 2 strides to breathe out, or whatever works for you - I do different things depending on how fast I'm going and how tired I am!).
I find running outside physically harder - hills! - but mentally find the treadmill harder (although have got used to it this winter!!). I listen to podcasts as it helps make the time go (and I will often stay on a bit longer to get to the end of a segment). I used to run to music, but found the knowledge that songs are about 3 mins long too distracting strangely, whereas a podcast there's no real way of telling how much longer there is unless you can see the screen.
I don't know of an app that would speak to your treadmill, but I think there are some treadmills that you can programme for intervals? Depends what you're running on. I just keep an eye on my times, and speed up and slow down (I do a lot of mental maths when running as well).
I think there is a technique, but I also think you run how you run to a certain extent, it's quite difficult to change what comes naturally.
Biggest tip is to make sure you're wearing the right kind of trainers to support your knees especially, and a shit hot sports bra.