Install php5.6 on ubuntu

apt install python-software-properties
add-apt-repository ppa:ondrej/php

apt update
apt install php5.6

apt install php5.6-mbstring php5.6-mcrypt php5.6-mysql php5.6-xml php-imagick php-ssh2 php-memcached php-memcache

Apache2

a2dismod php7.2
a2enmod php5.6
service apache2 restart

Cli

update-alternatives --set php /usr/bin/php5.6