You can try looking on fanfiction forums. There are often sections dedicated to writers helping each other. For example, on Archive of Our Own (AO3), they have communities where you can post about seeking a beta reader. Another option is to check out Tumblr. There are many writing - centered blogs that might be able to connect you with a beta reader. You could also join relevant Facebook groups for fanfiction enthusiasts.
One place to find a beta reader for your fanfiction is Reddit. There are subreddits like r/FanFiction where you can make a post explaining what kind of beta reader you're looking for. Twitter can also be useful. Use relevant hashtags like #fanfiction #betareader. You might attract someone who's interested in helping. Additionally, some fanfiction websites themselves have a beta reading feature or a place to ask for one in their writer's resources section.
Chapter 309, "Then Come Die with Me!", is the clearest early answer because it turns Zhou Xu's situation into a concrete plot event. The chapter turns that into something concrete by moving from In the dim and damp underground room, only a single incandescent bulb...
Chapter 678, "The Biggest Connection in the Circle of Friends!", is the clearest early answer because it turns Jiang Mingyu's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The landlord stood up, maintaining his smile, "Fifty-eight thousand,...
Chapter 543, "Please Name Ten Things You Dislike About Su Yinwan", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event.
Chapter 253, "She Hit My Head Three Times, I Hit Hers Seven Times", is the clearest early answer because it turns Round Brain's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Wen Jiaojiao immediately lost her composure, leaping up from the bed...
Chapter 325, "Miss Jiang, What Do You Think?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Xiao Yu cleared his throat and said, "So, Miss Jiang, our interview...
Chapter 277, "Jiang Yan Really Has a Youthful Vibe", is the clearest early answer because it turns Zhou Xu's situation into a concrete plot event.
Chapter 500, "Nearing Home Brings More Fear", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The room, white and gleaming, was filled with a faint smell of...
Chapter 410, "There's Something Wrong with This Lottery Box!", is the clearest early answer because it turns Something Wrong's situation into a concrete plot event. It opens with Nina's voice had barely fallen when Pan Xing turned his gaze to Jiang...
Chapter 227, "There's Something Wrong with This Stepmother", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Your Four Pillars of Destiny is very strong, with wealth, authority,...
Chapter 391, "Has another top celebrity had a scandal?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on You were born in a rural area, not exactly poor, but not particularly...