Check manualsLIB website or contact your dealer, they will give it to you, or check KR-MOTORS website (Hyosung Official website), click their GV300S bike models , and they should have a page that says “manuals” Some one on the forum has already done valve clearances tutorial on their GV300S , if you search for it
Searched KR motors website and manualslib, no service manual exists for this bike.