I'm not sure how 'Line' is pronounced - if it is like the English name Lynn, Lyn, Lynne, then Pete's answer is correct, tho' it will be pronounced by Thais with a rising tone at the end with the spelling หลิน. If you want it pronounced without a tone, spell it as ลิน If your name is pronounced the same as the English word 'Line' (and the same as the last syllable in 'Caroline' you need a different spelling. There are several ways to do it, ไลน์ or ใลน์ or ลัยน์ or ลายน์ should all work.

Hi you name can write in thai as หลิน and pronouced lin'