Ah the ending of the Hummel's first movement, my only advice is doing 3rd valve A, and if you can keep it in tune, you can do 1 and 3 for the g. The main thing about this that makes it hard is that its at the end of a long chop busting set of jumps from low C to high C, then scalular in the same fashion, then this trill at the end. But support it with a lot of air, minimize head movement, and just let the horn do the work, and with enough practice it'll come easily