Important: if you are looking to enter in paper survey responses, please use Data Entry Mode: Using Data Entry Mode to Manually Add Responses
To update the "Require login if duplicate responses seen from same IP" setting for all your projects, on the left hand pane of your Engagement Dashboard, click the Settings icon (gear.)
Once on the setting tab, uncheck the box that says "Require login if duplicate responses seen from same IP."
This will allow multiple people to respond using the same IP address (or device).
Enable or disable this for a specific project or survey:
Go to the project's 'Settings' tab, and toggle the "Require login if multiple responses received from same IP address" switch.