Go to Analyzer NX > Tools > Tags > Main tags > xtcore.js file (deprecated) > Domain Cookie lifetime
The lifetime is in days.
Go to Explorer > Data Quality > Data Collection Portal > Tagging > Tag Composer
Click on the scroll wheel for identified visitors and change the value for identified visitors data lifetime. The lifetime is in days.
Once the new version of the file is downloaded, you need to implement it into your site so that the updates are taken into account.