The steps for contractual private investors to apply to the court for sealing up the frozen fund custody account are as follows: entrust a lawyer to draft an application, submit it, the court will review it, and seal up the frozen account.

1. Entrust a lawyer to draft an application: Investors need to entrust a lawyer to draft an application, detailing the reasons, basis and request for applying to close the frozen fund custody account.

2. Submit an application: Investors need to submit an application to the people's court with jurisdiction and submit relevant materials required by the court, such as identity certificate, investment contract, fund share certificate, custody agreement, etc.

3. Court review: The court will review the application, verify the identity and capital contribution of the applicant, and decide whether to accept the application according to law.

4. Seizure and freezing: If the court accepts the application and considers it necessary to seize and freeze, it will issue a seizure and freezing order, requiring the fund custodian or relevant institutions to execute it immediately and freeze the funds, shares and other related assets in the fund custody account.