I experienced the similar situation at week 32 and growth scan showed AFI only 7.6cm. My gynae noticed me and I started to increased water intake after that. 1500-2000ml plain water, 1 piece fresh coconut juice and some more soybean milk or fresh milk on daily basis. Today week 35 Im asked to redo the growth scan and liquor amount is back to normal, AFI is 12.3cm. I was so so excited！
Drink more plain water . I had this issue too . But after that mangae to increase.
Try upping your water intake. Take care mama ❤️