Use a MAC (Mean Aerodynamic Chord) calculator to find the MAC and then put the CG at 18% of the MAC and just extend that to the wingtips so you know where to put your fingers.

Flying wings provide their own stability so you need to do the CG differently. On any flying wing under no circumstances should the CG ever go further back than around 23 to 27%. Even with that range the model would be pitch neutral. Further back than around 27% and it'll want to swap ends. Normal CG ranges for flying wings is around 18 to 22% of the MAC.