non-programmer wanting to learn needs help to modify "AddAISetRevPX.groovy" to company rev scheme

I need help to revise the sample groovy script that oracle provides to set the next rev of the affected items of an ECO.

Our rev scheme is a 3 digit numeric.  Example: 001, 002, 003, ... how can I modify the section of the grovy script to set the next number to 001 if it is the first rev and increment the non zero portion to the next number.

Below is the portion of the code where I beleive I need to revise.

Than you in advance for your teaching!!

   //find the number part of the old rev on the right
             for(int i=revLength-1; i>=0; i--) {