If you can't reach the dashboard, switch themes in phpMyAdmin. First, know the folder name of a working theme (e.g. twentytwentyfour) in wp-content/themes.
- In cPanel open phpMyAdmin and select your WordPress database.
- Open the
wp_optionstable and use search to find the rows whereoption_nameistemplateandstylesheet. - Edit both rows and set
option_valueto the working theme's folder name. - Save and reload your site.
Note the table prefix may differ from wp_; check wp-config.php. This is handy when a broken theme causes a white screen. Once you can log in, switch themes normally under Appearance > Themes. Need a hand? Open a ticket.