Have you ever performed DEDECMS? Can you help me? What should I do?

Have you ever performed DEDECMS? Can you help me? Why is the prefix __used before the table name of DEDECMS? How do I replace this prefix? I didn't find it in the source code. in the configuration file, have I ever performed DEDE CMS in the dededesql. class. php file in the include folder? Can you help me?
Why is the prefix __used before the table name of dede cms? How do I replace this prefix? Not found in source code

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In the configuration file
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SetQuery function in the dedesql. class. php file in the include folder