hi buddy....most of the time at this step of seedling this can be caused by an overwatering...so it slow down nutes absortion in a slight lock out process so the plant can't correctly absorb nutes (and N).... normally u have to wait for a dry cycle....but as she's so fragile she could die during this time
A tip wich can save her..... make slowly with great care with a wooden pic for example... holes all around main stem...to bring more oxygen directly in roots....to help them recovering 🙏
hope this help and good luck 👊