Just run the setup script as follow:

 # /var/www/imscp/engine/setup/imscp-setup --reconfigure

If you want to specifically change something such as the main IP address for the control panel, you can use directly the ips flag and just answer the questions.

# /var/www/imscp/engine/setup/imscp-setup --reconfigure ips

This will cause all questions already seen to be show again.