You must file form 5500 by July 31st if the balance in the account was more than $250,000 Dec 31st of 2019.

If you have a 401K and manage it yourself, the Form 5500 Series is an important compliance, research, and disclosure tool for the Department of Labor, a disclosure document for plan participants and beneficiaries, and a source of information and data for use by other Federal agencies, Congress, and the private sector in assessing employee benefit, tax, and economic trends and policies. The Form 5500 Series is part of ERISA’s overall reporting and disclosure framework, which is intended to assure that employee benefit plans are operated and managed in accordance with certain prescribed standards and that participants and beneficiaries, as well as regulators, are provided or have access to sufficient information to protect the rights and benefits of participants and beneficiaries under employee benefit plans. Read more here