about repair a database file of MS SQL Server 6.5 ?

Now i must restore a database from a backup file of MS SQL Sever 6.5,
but this file is bad. When i restore database from this file, SQL Server tell me that the format of this file is not file format of SQL Server 6.5.
So that I must repair this backup file firstly. I don’t know database file format of SQL Server 6.5. I want to get some helps from experts in this forum.
Thanks a lot in advance !