First ensure you have imagick installed via yum:

yum install ImageMagick ImageMagick-devel

If installed then run:

/opt/cpanel/ea-php56/root/usr/bin/pecl install imagick

or install it through the module installer via WHM.

Once done add the following to php.ini or via MultiPHP Editor via Editor Mode right at the bottom of the file and save:

extension=imagick.so

All done.