You will need a new KR2 from the amphur. Although it sounds like a cop-out answer, I would advise getting in touch with your Immigration office to see what their requirements are as they all differ quite a bit.
B. Your employer will prepare the paperwork and will post this to you (some embassies will allow for the paperwork to be emailed to you and you can print this off, most want originals)
C. Take the paperwork to your nearest Thai Embassy/Consulate and request a Non B visa. (now, owing to covid there are several other requirements to enter Thailand and no one can currently enter from India due to some pandemic issues).
C. IN NORMAL TIMES, enter Thailand with the NonB (90 days) and your employer will then apply for the work permit on your behalf at the ministry of labour.
Contact your nearest consulate/ embassy for the latest entry requirements.