Orientation to the 5th and Octave, Exercise No.7 from my book Exploring the Fretboard: 100 Exercises for Intermediate Guitar. PDF sheet music with notation, left hand fingering, and video lessons. This book offers students a set amount of ordered material and a variety of ways to investigate the fretboard. It has been designed as an exploratory primer before further and more comprehensive study.
Remember to say the note names out loud. Practice only one exercise at a time for 2-3 minutes a day. Repeat the exercise for a few days even if you can play it first try. This exercise will solidify the 5th and octave for each open string and build some anchor points at the 7th and 12th frets.
Here is the YouTube link if you want to watch it there.