@AskLibreOffice I cannot use a @MySQL table on Versión: 4.2.6.3 of @libreoffice, I use #jdbc connection. Check image.
Your description is vague, nevertheless I’ll try to help. Goto Tools > Bibliography Database. You get a new window showing the default database. In that window, menu Edit > Choose Data Source. All registered data bases are shown. Select your MySQL one. That implies, that your data base needs to be registered.
Make sure that the field names in your MySQL data base are the same as in the Bibliography data base. Find the names in DeutschEnglischBibliography - Archiv des LibreOffice- und OpenOffice.org-Wiki. That is in German, but the right column lists the English field names. In case there are two entries in a cell, you need the second one for your own bibliography data base. The names are case sensitive.
If that does not help, you must improve your description.