Marjan,
Since the version of the DB2 server is too old to be supported by SQL Server Migration Assistant and other tools like Azure Data Factory, plus the organization is not considering to upgrade that version of the DB2 server, then the solution I will propose to you is to export the data as text delimited format or CSV, upload it to an Azure Storage Account, then import that data to Azure SQL Managed instance using tools like bcp, Azure Data Factory Copy Data Tool, or use External Tables.