You can't. Visa or MasterCard credit cards can be used almost everywhere in Iceland (UnionPay cards are rarely accepted), and there is basically no need to bring cash. Iceland is a country with highly developed credit card applications, comparable to domestic Alipay WeChat payment. You can get a card in the last bathroom without changing cash. There is no bank in China to change, and there is no need to change it at Iceland airport. Iceland is not a tipping country either. Occasionally, those who need to tip can pay with small change in dollars and euros. Credit cards are personal belongings and should not be lent to others casually.