Dear @Touhidul.Islam,
Assuming you are using a recent version of OpenFAST, the reference position of the potential-flow solution is user-specified via PtfmRefxt/PtfmRefyt/PtfmRefzt in the HydroDyn input file. So, you should be able to set this point to the body CoG and use your data directly (as long as it is in WAMIT data format).
Nevertheless, if you want to shift your potential-flow data from the CoG to a different point, such as SWL, see a related forum post: Time domain analysis by AQWA.
Best regards,