554xl accu bale monitor learn bale size

The bale size say's 4 after I dump a bale,  I can't get it to go back to zero like it always said.  

 

I had a problem with the main plug,  it didn't have a good connection and almost came unplugged while it was running, then I started having that 4-20 on the size instead of 0-20 

 

 

I had to run the full bale size from 20 up to 26 to get a 5 foot bale,  it maxes out at 29

 

 

 

how do I "learn" it back to zero? 

 

 

the accu-bale manual is gone

554xl accu bale monitor learn bale size