If you do not tell Limesurvey to save the IP address, it won't save the IP address. Simple like that. When activating your survey, there are a couple of settings presented that you need to choose.
This is the screen you see when activating your survey. "save IP address" defaults to "No". If you don't switch to "Yes" the IP address will of course not be stored.
This is what you see on the "Notifications & Data" page of your survey when you did not tell Limesurvey to save the IP address upon activating.
If you want the IP address to be stored, the only way to do this is deactivating the survey and activate it again with the correct settings.
Note: When deactivating the survey, the response table with the already collected responses so far will be archived. Usually, upon reactivating you can import this old response table again (but of course you won't have any IP addresses for the responses collected before you change the setting). However, I personally download the responses collected so far, just to be save. What you have, you have. If something goes wrong, you can join the different data files later outside of Limesurvey. I like to play it save.
If the current responses are just tests, then it doesn't matter.