You can start by looking on popular fanfiction websites such as Archive of Our Own (AO3). It has a large collection of 'Harry Potter' fanfiction, and you can use the search function to specifically look for TF (transformation) related stories. Another option is FanFiction.net, where you can filter the 'Harry Potter' category and then search for transformation themes within those stories.
You could also ask other 'Harry Potter' fans directly. If you know someone who is into 'Harry Potter' fanfiction, they might have some great recommendations for 'Harry Potter TF fanfiction'. Attend fan conventions or local 'Harry Potter' meet - ups if possible, and strike up conversations about fanfiction. You'll be surprised at how many hidden gems people can point you towards in the world of 'Harry Potter TF fanfiction'.
Chapter 43 is the strongest chapter-level answer because it starts from The moment He Yun willingly sat next to Jiang Li and even took off his... and follows through on Just as she turned her gaze away, the other party huffed and withdrew her....
If you want the clearest chapter reference, go to Chapter 49. Early on, My phone!!!" Jiang Yan's roar echoed continuously through the mountains in...; later, the chapter leans on Watching helplessly as his latest-model phone was taken away by a....
Chapter 82 is the strongest chapter-level answer because it starts from Jiang Li gave her a fleeting glance. and follows through on And so, aside from Wen Jiaojiao, the remaining five set off, each....
If you want the clearest chapter reference, go to Chapter 54. Early on, Five minutes later, the people of Chixia Village, who had received the...; later, the chapter leans on Leading them was the village chief himself..
Chapter 43 is the strongest chapter-level answer because it starts from The moment He Yun willingly sat next to Jiang Li and even took off his... and follows through on Just as she turned her gaze away, the other party huffed and withdrew her....
If you want the clearest chapter reference, go to Chapter 37. Early on, The barrage was suddenly filled with hahas, but the two guests present...; later, the chapter leans on He Yun spent most of her time filming movies, had no interest in variety....
If you want the clearest chapter reference, go to Chapter 40. Early on, [Jiang Li claims she copied this herself?; later, the chapter leans on But her calligraphy is actually this pretty?] [Jiang Li dares to boast,....
A practical answer is Chapter 78, because it turns the idea into a concrete scene. The chapter opens with He Yun, too, tidied up and walked over to rest in the shade of a tree., adds pressure through That weed whacker is obviously mine!, and ends on [HAHAHA, is it just me or does Movie Emperor He.
Look to Chapter 72 for the clearest answer. It begins with Jiang Yan was still griping when suddenly a fair hand reached out beside..., keeps building through I'll take these, thank you." In an instant, five pairs of eyes stared over..., and lands on Think about it." Jiang Yan fell silent..
The best chapter pointer here is Chapter 88, "I Call This a Test of Your Will!". It opens with She wanted to refuse, but didn't have the courage to do so. and closes on Let's go," Jiang Li said in a soft voice..