Contact Merrill Lynch - if they are managing the 401K, then they may be the "plan administrator". If not, they will know who the plan administrator is and how to contact them.
From Who Is My 401(k) Plan Administrator?
Asking Human Resources is typically the most straightforward way to find your 401(k) administrator and figure out who manages your retirement savings account’s day-to-day activities.
The employer is almost always the plan sponsor. Typically, the sponsor hires a third-party administrator to oversee the accounts. Sometimes an individual, internal board, or appointed group of trustees will serve as the plan administrator. From a risk management standpoint, the employer should not double as both sponsor and administrator.
If you have a Summary Plan Description handy, you can easily check who signed the return as the Plan Administrator. At the Department of Labor’s website, you may also search, request, or download a copy of Form 5500.
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