Can you do it without the trumpet? Take your breath, then Ku Ku Ku Ku — quarter notes at 60? (or even just one Ku)
If you can do it with just your breath (BCH) and trading the Tu for Ku, then add the mouthpiece. If that’s working, add the leadpipe. Hopefully, your Ku is going ok using the lead pipe. Then add your trumpet — start with the mouthpiece (assuming you can Ku with the mouthpiece) and bring your trumpet to the mouthpiece — just open low C or second line G.
But get it going first with just your breath — no mouthpiece or trumpet.