You do not get severance if you quit. Nobody is automatically entitled to any severance legally, ever, unless you were hired under a contract such as a 1099 employee and you have severance written into your agreement. Standard W-2 employees usually do not get severance.
Neither the California Labor Code nor the federal Fair Labor Standards Act require employers to offer severance agreements to departing employees. Instead, severance agreements are provided by employers to accomplish a specific goal.
Some factors that are often considered include length of employment at the company, your position or rank within the organization, salary, and individual circumstances relating to termination. Some employers adhere to a written contract or employment agreement or policy that was outlined previously.
All you can do is ask. They'll probably say no but you're bound by the companies severance policy/program but legally it's not a required benefit. BUT keep in mind the company wants you to sign that agreement at the end of the day so you could get more. You could try and use trigger words during your conversation.
Present the employee with the severance agreement, worked on by your HR manager, and walk through each section. Leave time for the employee to ask questions and make clear the time frame during which the employee has time to meet with their lawyer, as well as their last day.