Conditional clause for early release

Hi, My notice period is of 90 days and I noticed my employer that I need early release in about a month. As per my company's employee handbook for termination of service is : "Should the employee desire to leave the Company at any time, the permanent employee will be required to give 3 (three) months’ notice in writing to the Company or 3 (three) months basic salary in lieu thereof. If employee decide to leave the company by paying notice pay, then he must bear the tax liability. The Company also reserves the right to terminate the services of an employee if he/she is guilty of any misconduct or breach of duty, without any notice period." But my manager asked me to get replacement for my position and after onboarding replacement provide 1-week training. I agreed to it that I will try my best and shared replacement too, and now they are delaying in interview process and also asked me to serve notice period of 90 days if there is any deviation from our agreement. What should I do, as my offer with another company will be withdrawn if I do not join by provided joining date.