How to uart4 used as a normal serial port

how to make the uart4(H9、H10)used as a normal serial port?
In the Datesheet of TX1 ,H9 UART3_RX H10 UART3_TX .but in OEM file of TX1 ,H9、 H10 RSVD.

anyone can help me? thanks

Hi, they are RSVD, please do not use them.