Let's review the Low E string's natural notes. Eventually, these will become second nature to find and play, and you will know them as easily as the open strings notes.
Start with an open low E, then fret each natural note, ending on the 12th fret.
1st Fret = F
3rd Fret = G
5th Fret = A
7th Fret = B
8th Fret = C
10 Fret = D
12 Fret = E