Add below CSS code to center-align the text in all cells of the Advanced Table module.

.dipl_advanced_table .dipl_advanced_table_item_cell {
    text-align: center !important;
}

.dipl_advanced_table .dipl_advanced_table_item_cell p {
    text-align: center !important;
    margin: 0 auto;
}

Where to add the CSS

You can add the CSS in any of the following locations:

• Divi → Theme Options → Custom CSS
• Appearance → Customize → Additional CSS
• Your child theme’s stylesheet (style.css)