When you are so close to the approval of I-485, I would suggest to stick with the same employer. But if you still decide to switch the employer, your new employer need to immediately fill the Request for Job Portability Under INA Section 204(j) form which is available at USCIS site.
https://www.uscis.gov/i-485supj

Disclaimer:This is for informational purpose only. You should not rely on anything you read here to make decisions, Please consult with Immigration Attorney.