It is the 30013 that is not correct, it is the address of the register, but not the Modbus address.
Seemingly there is a base address of 30001 (which corresponds to Modbus 0).
30013 becomes 000C (see page 15 of the pdf you posted a link to).
as a matter of fact 30013-30001=12 → 0x000C
The syntax should be something like:
/iot modbus transceive address=111 function=4 data=000C0002
(for some reasons that device seems to need an even number, so 1 register=02, 2 registers=04, etc.)
data is the actual hex string
values is a comma separated array of decimal values, check:
https://help.mikrotik.com/docs/pages/viewpage.action?pageId=61046813
using values, it would probably be:
/iot modbus transceive address=111 function=4 values=0,12,0,2
See also this thread:
http://forum.mikrotik.com/t/knot-modbus-rtu-write-registers/177356/1