At the Shanghai Pudong Airport, there are buses from the airport to Yiwu. You can take it at the parking area of bus on the second floor of the parking lot of the departure hall. The bus departs at 13:10 or 16；50. The ticket costs CNY180. Additionally, you can take the airport bus to go to the railway station of Shanghai and take a train to Yiwu. Please refer to this site for the details of Shanghai:

https://www.travelchinaguide.com/cityguides/shanghai/getting-there.htm