In your Xampp folder, open php.ini
file inside the PHP folder i.e xampp\php\php.ini
(with a text editor).
Search for extension=mysqli
(Ctrl+F), if there are two, look for the one that has been uncommented (without ";" behind)
Change the mysqli with the correct path address i.e extension=C:\xampp\php\ext\php_mysqli.dll
.
On your Xampp control panel, stop and start apache and MySQL