In order for the plan to offer passively managed funds, the plan sponsor (employer) or whoever makes decisions on behalf of the sponsor, would need to choose to include passively managed funds in the plan. They would then need to connect with the vendor partner who helps in this process, and include such funds on the platform.
One other option would exist if the plan offers what is called a brokerage window. If the plan offers participants a brokerage window, you could move some or all of your plan balance to this brokerage feature, and choose from an additional array of funds and/or securities. These may include passively managed funds.
If you are willing to share the name of your employer, we can do some research for you, and let you know what your options are.
Hope this helps.