Use Supplement J to:

Confirm that the job offered to you in Form I-140, Petition for Alien Worker, remains a bona fide job offer that you intend to accept once your Form I 485, Application to Register Permanent Residence or Adjust Status, is approved. Beginning Jan. 17, 2017, if you are filing or have previously filed Form I-485 based on being the principal beneficiary of a valid Form I-140 in an employment-based immigrant visa category that requires a job offer, you will need to file Supplement J instead of submitting a job offer letter;
OR

Request job portability under INA section 204(j) to a new, full-time, permanent job offer that you intend to accept once your Form I-485 is approved. This new job offer must be in the same or a similar occupational classification as the job offered to you in the Form I-140 that is the basis of your Form I-485. (For more information about how USCIS determines which jobs are same or similar please see PM-602-0122: Determining Whether a New Job is in “the Same or a Similar Occupational Classification” for Purposes of Section 204(j) Job Portability (PDF, 205 KB) (March 18, 2016) (PDF, 205 KB)

Source:https://www.uscis.gov/i-485supj