you take the plate/cover off the end of the head shaun (easier with the mount off) and there will be some skidmarks on the nylon tensioner,
if they,re very deep ruts a new or better tensioner would take up some slack, but its usually just a stretched chain tbh
and if you hold one of the cams with a spanner you can turn the crank pulley back and forward to assess how much slack the chains have