Find "php.ini" within your directory by following these steps: Open any text editor to the PHP folderxampp\php\php.ini (using any text editor).
Use Ctrl+F to find extension=mysqli, or if there are two entries, identify the one that is uncommented (without ";" at the beginning).
Next, you have to update your mysqli line with the correct path, which can read the extension=C:\xampp\php\ext\php_mysqli.dll.
After that, launch your Xampp control panel, and then stop and restart both Apache and MySQL.