Round and push your lips forward first, as if about to whistle.
Press the tongue blade to the ridge area, like a "t" made slightly further back.
Release slowly so the stop melts into a "sh": one single sound, not two.
Keep your throat silent all the way through.
Now say: chin, church, match.
✅ Check
Say "chin" then "gin" with a hand on your throat. "chin" is all air; "gin" buzzes from the start. And check a mirror: your lips should be rounded for both.
⚠️ Common trap
Forgetting the lip rounding. With flat, spread lips, /ch/ turns thin and sharp and stops sounding English. Push your lips forward before the sound starts, not after.