Download SeTool2Lite 1.1. Install Usb flash driver. Identify it.
If it is EROM CID49, or EROM CID51, upgrade to CID52, using XS++ 3.1. Then read B. How to apply the generated patches to DB2020 CID52 phones, here:
Remove SIM-lock patch generator - Top Sony Forums.
If it is EROM CID53, things are more complicated:
ANYCID patching - Top Sony Forums