how would i modulate from Ab to Bb?

i’m writing a song that goes from Bb in the intro and verses, to D in the pre-chorus, to Ab in chorus. how would i modulate from Ab to Bb, after going from chorus to verse?

for the pre-chorus, i managed to go from D to Ab through:

D6 - Em9 - Gmaj7 - Gmmaj7 - A - A#dim7 - Bm - E - Cm - C7

then Cmaj7 - Cmmaj7 - Ab - C7 etc..

what might work in modulating to Bb after the Ab chorus? i’m stuck.