Hi there! I thought about how a three step melody works. For example, if I were to take three notes B-C to D you can tell the middle note must act like a passing note. So I thought there must be a passing chord. For this melody I thought what if I played a B dim chord since that was my starting note in this melody and I was ending it with the D note and that didnt sound right. I thought about how about a D chord since I thought to myself since I started with the B note and ended the melody with a D note I thought I mighest well play a D chord, but it never seem to fit, but when I played B-C to D and I played a C chord since the C note was in the middle in between B and D it sounded good, but I guess since the C note is in between B and it might act as a passing note because the C is acting like a passing note to get to D. So it starts with B-C to D and ends with D. So I tried with the rest of the melody like this and this is what I got:

B-C to D - Cmajor or a Cmaj7
C-D to E - D minor or a Dm7
D-E to F - Eminor or a Em7
E-F to G - Fmajor or a Fmaj7
F-G to A - Gmajor or a G7
G-A to B - Aminor or a Am7
A-B to C - Bdim or a Bm7b5

I even tried this method with the pentatonic note a three step melody and choosing the middle note that act as a passing note to get to the next note.

A-C to D Cmajor
C-D to E Dminor
D-E to G Eminor
E-G to A Gmajor
G-A to C Aminor

At the end, the middle note in a three step melody acted as a passing note, then I thought I mightest well play that middle note chord and it sounded good. But when I think about it, it's only for one chord if you two chords you'll have to increase the melody to four notes which creates this time two passing notes for two passing chords which this time creates a chord progression.