playing the song in C [C,F,Dm,G,D7,A] 
using a bar chord for Ab [G], 
and not worrying about the [Gb/A] just play it without the A. 
Intro
Db

Verse 1
Db
Jingle bell jingle bell jingle bell rock
                       Gb
Jingle bells swing and jingle bells ring
Ebm
Snowing and blowing up bushels of fun
Gb                 Ab
Now the jingle hop has begun

Verse 2
Db
Oh, Jingle bell, jingle bell, jingle bell rock
                      Gb
Jingle bells chime in jingle bell time
Ebm
Dancing and prancing in Jingle Bell Square
Gb         Ab     Db
    In the frosty air

Chorus 1
       Gb
What a bright time, it's the right time
   Db
To rock the night away
       Eb7
Jingle bell time is a swell time
Ab
   To go gliding in a one-horse sleigh

Verse 3a
Db
Giddy-up jingle horse pick up your feet
                  Bb
Jingle around the clock
Gb                      Gbm/A
Mix and a-mingle in the jingling feet
Eb7        Ab          Db
That's the jingle bell rock

Interlude
Db / / Gb / Ebm / Gb Ab Db

Chorus 2
Gb
What a bright time, it's the right time
   Db
To rock the night away
Eb7
Jingle bell time is a swell time
Ab
   To go gliding in a one-horse sleigh

Verse 3b
Db
Giddy-up jingle horse pick up your feet
                  Bb
Jingle around the clock
Gb                      Gbm/A
Mix and a-mingle in the jingling feet
Gb           Ab
  That's the jingle bell
Gb           Ab
  That's the jingle bell
Gb           Ab          Db