Looks like OP wanted to know how to send register address, if so it would be like this
Writting to register
I2C1_Init(100000); // initialize I2C communication
I2C1_Start(); // issue I2C start signal
I2C1_Wr(SLAVE_ADDRESS); // send byte via I2C (device address + W)
I2C1_Wr(write_register); // send byte (register address) *Register address here from page 20, look into list and see what address you want to write to,
I2C1_Wr(0xAA); // send data (data to be written)
I2C1_Stop(); // issue I2C stop signal
Reading from register
I2C1_Start(); // issue I2C start signal
I2C1_Wr(SLAVE_ADDRESS); // send byte via I2C (device address + W)
I2C1_Wr(write_register); // send byte (register address)
I2C1_Repeated_Start(); // issue I2C signal repeated start
I2C1_Wr(SLAVE_ADDRESS + 1); // send byte (device address + R)
read_value = I2C1_Rd(0u); // Read the data (NO acknowledge)
I2C1_Stop();