"Mother, I have some pleasing news. I was / have been [BrE] selected by Mr. Walton to fly to California for the showcase of the 'Whistler's Mother', which is soon returning back [k3: redundancy – 'returning' already implies 'back']returning to the US."

"That's wonderful Bean, but it sounds like a handful of work! You have never flew [k4: incorrect tense – 'have' + past participle]never flown out of London, let alone the UK. And on top of that, you know nothing about American art or its history."

"I suppose you're right, however, Mr. Walton has said that he'll assist me to develop [k4: incorrect verb pattern – 'assist someone in doing something']assist me in developing  / help  me develop a speech worth presenting, and with that source I will quickly catch on on [k4: repetition – only one 'on' is needed]catch on all of the shenanigans. [k2: sense - What and whose shenanigans would Beany need to catch on? Had they already taken place? Judging by the use of 'catch on' thay had.] /May be you meant: to prepare for any possible questions

"Hmm... that's true. You've always been quick to catch on little things, but a whole speech? [k3: informal construction – consider making this more complete]but preparing a whole speech might be a different challenge. That might be a bit more than you can chew. And to whom will you be presenting this speech?"

"I will be presenting at the LA gallery."

"Well then it seems like you've got it all figured out. Although, I do want to know whose bank accounts will sponsor this trip / who will be funding this trip."

"Oh, well [k5:syntax], No worries! That's all covered for by [k4: 'covered by' is the correct form]covered by the folks in California."

"Oh, that's just wonderful! My little Bean is all grown up. You're going to be great, there's no one better for this position than you [k3: more natural alternative suggested]you're the perfect fit for this opportunity."

👍 Very good!