So... if the song is in the key of C major..... and your chords are C.... F....G with Am....

determine if you are going half a step or a whole step or something else.

You said key of C that changes to the key of A.

C F G are the 1 4 5 of that key.... Am is the 6minor

In A you have A D E with F#m being the 6 minor in that key.

Just enter the following F#m and it should do what it needs to do.

remember that BB will let you enter chords for a song in a variety of different ways.

BTW: It really helps you if you do get a basic understanding of music theory. At least to the point that you know what the 1 4 5 chords are in a given key.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.