Welcome to Microsoft Q&A forum.
As I understand, you want to Copy Database in Azure Managed Instance.
This could be done through 3 methods: Azure Portal, PowerShell and CLI as illustrated in the below link:
As per the existing documentation, you can perform copies of Azure SQL Single and Pooled Databases only by COPY command https://learn.microsoft.com/en-us/sql/t-sql/statements/create-database-transact-sql?view=azuresqldb-current&preserve-view=true&tabs=sqlpool#database-copies
Refer to https://learn.microsoft.com/en-us/sql/t-sql/statements/create-database-transact-sql?view=azuresqldb-mi-current&preserve-view=true&tabs=sqlpool for Azure SQL Managed Instance.
Let us know if above information helped or you have a different ask.
Thanks