Wa alaykumu salam wa rahmatullahe wa barakatuhu
I do not know any app.
Classic mindfullness as Budhist/Zen/Yoga is not common in Islam.
There is most common known dhikr.
For beginning read the dua from ayah 71:28 at least 10x mornings and evenings.
Better 33 or 100x
Also Shukrulillah (think about many blessings).
Google for grattitude (also modern science articles done).
You should probably start from salat.
Learn additional duas in salah.
Increase nawafil.
Pray dyas mornimgs, evenings and before sleep, comming and leaving home.
There is a dua book momin ka hatyaar in English.
And read this recommendations:
https://www.islamicboard.com/general...ml#post3043204
It will be enough for start.
And spread dua books and dhikr among family, friends, neighbors and online.
InshaAllah it will add to your amal.