Best get it fixed soon, remove air filter then rocker cover ul see push rods and rockers simply remove all bolts with 8mm head and rockers will lift of, strip rockers of shaft placing rockers and springs on card or bench in order thy came of until u come to the one that is worn and replace the just rebuild in reverse
Sorry don’t have valve clearances to hand or bolt torque, if noise persists then came may be worn also and that’s a much bigger job
bert, August 2004