Luis,
As Guillaume mentions start with just the lead pipe. Blow the mouse piece by releasing the air then inserting into the lead pipe and don’t change the flow(volume) or anything. It will eventually pop out.

Another way I practice is on Largo Long Tones(or any long tone exercise). Do the exactly the same approach but hold your trumpet and whatever keys down(start on middle C) with your right hand, then with your mouthpiece in your left hand hum the pitch, then ah-oooh(blow air), apply the mouthpiece to your chops(continue only blowing air- no buzz), then gently slide the shank into the lead pipe on the trumpet. Again, a full/resonant sound will come out eventually. Go back/forth by inserting/withdrawing the mouthpiece in both scenarios and make sure only air comes out when the shank is disengaged from the lead.

Hope this helps.
Robbi