If you change your mind about leaving after discussing the job offer with your boss, it's important to communicate this as soon as possible. Reach out to the company that offered you the new job and inform them of your decision. Then, have a conversation with your boss to explain your change of heart and your desire to continue working at your current job. Be prepared for the possibility that your boss may have concerns or reservations about your commitment moving forward, so be prepared to address these issues and reassure them of your dedication to the company.