It is very easy to crease the large part your bell flare. The rim is very large and exposed in comparison to the rest of the tubing, and the flare is thin and soft. Any kind of bump, drop, or undue pressure on the bell flare can cause it to bend and crease. And if that happens, you should never try to undo those creases by yourself.
It is tempting to grab that flare and try to fold the metal back in place, but do NOT do it. Live with it until you can get it to a competent repair tech.
Once you crease that flare, the metal becomes hardened along the creases. If you try to undo the damage the harder metal at the crease will not give way and unfold. The softer metal near the crease will bend first, actually causing a secondary crease. Both the creases will be hardened, now. Your technician will not only have a more difficult time fixing the bell flare, but the bell will have a larger area of hardened metal than necessary.
Your technician will use tools to flatten and unfold the creases right along the crease lines. The metal may become hardened at those folds, but that will be held to a minimum and the result will be optimal if repaired correctly.
Dave and Chris are brass technicians who enjoy helping players get the most out of their playing experience.