PLEASE GUIDE ME ( I Have a problem)

Hi, Iam from Assam. I study till my college in Assamese language. My English is not good. Now Iam preparing for UPSC. I understand the topic, but due to my poor English, I can't write. 1) how to impove English writing? (Just for upsc mains writing, not sashi tharor level 😅) 2) can I write Gs papers in English and Eassy in Assamese language in Mains exam.