Songwriters who aren’t trained in music theory often hear a song using a bass line movement descending from the major root chord to the relative minor, then imitate that movement in their own songs this way: (key of C) C, B minor, A minor. In the Nashville Numbers System that would be 1, 7-, 6-.
What they are actually trying to imitate is this: C, G/B, Am or in Nashville Numbers speak: 1, 5/7, 6-. The G/B means a G chord played with a B bass note. If you play guitar or piano and you’re solo you can make the movement happen by voicing the deepest pitched B note as your root for the G chord. But if you’re working with a bass player it’s fine to simply play the full G chord and let the bass player take the B bass note. Another example just to confirm you understand the concept, this time in the key of G : Instead of G, F#m, Em use G, D/F#, Em- b.e.