How to Flash back Wanhao firmware?

Hi, I’ve decided to use retailer’s service and I need to get original firmware back. I’ve tried to find some instructions, but i haven’t found it. Could you please give me a link if it is existed. My printer is Di3+ v2

You mean a Mark II? Have you tried on the Wanhao website. I think they have binaries.

Here is a link to the firmware from Wanhao. Be sure to grab the correct one for your printer. They have files for both the original Di3+ and the Di3+ Mark2 on that page.