Watch the Alternating Bass: 3 online guitar lesson by Muriel Anderson from 1-2-3 Fingerstyle Guitar

On a C chord, alternate the third finger of the left hand from the 5th string 3rd fret (C note), to the 6th string 3rd fret (G note). That has the bass going back and forth between the root and the fifth, rather than between the root and the third, which is a more typical sound for fingerpicking.

Likewise on a B7 chord, alternate the second finger of the left hand from the 5th string 2nd fret (B note), to the 6th string 2nd fret (F# note).