The increase of foreign exchange reserves is a surplus of foreign trade, which means that the income from selling products abroad in China is greater than the funds paid for importing products from abroad.

There is no inevitable relationship between RMB appreciation and foreign exchange increase. Appreciation is only relative to foreign currency appreciation, and it may also be caused by foreign currency depreciation, for example. There may be many reasons for appreciation, such as politics. The reason why the United States wants the RMB to appreciate is that if the RMB appreciates, China people can buy more products made in the United States, thus transferring the wealth of the whole society to the United States.

There is no fixed relationship between the two, but there is an indirect relationship.