Error 602 in database in MSSQL

Hello! Please help! I am trying to upload database from old computer to the new one and I see some weird error that I haven't seen before: Error 602: Could not find row in sysindex for database ID 7, object ID 1, index ID 1. Run DBCC CHECKTABLE on sysindexes. What does this mean? what is DBCC CHECKTABLE? How to fix it? Thank you in advance
