OK, so I checked the data sheet and it says,

The I2C embedded inside the LIS2DH12 behaves like a slave device and the following protocol must be adhered to. After the start condition (ST) a slave address is sent, once a slave acknowledge (SAK) has been returned, an 8-bit sub-address (SUB) is transmitted: the 7 LSb represent the actual register address while the MSb enables address auto increment. If the MSb of the SUB field is ‘1’, the SUB (register address) is automatically increased to allow multiple data read/writes. [Emphasis mine]

but I still don't get what to do. How do I send the register address when the aforementioned function doesn't have it as a parameter?