All the Splunk Enterprise comes with trial license version for 60 days. After this evaluation period, those messages are shown. If you want to remove those messages, you have two options:
1 - connect your instance to Splunk License Master from your company
2 - Purchase a license for your personal splunk box
Note: If you select the option 1, please carefully about the data your are sending to this instance, because all the data that you indexed in your personal box will count against the company license, and maybe you can reach the day capacity license.
Please read this document where you can have more details about how splunk is being licensing.
https://docs.splunk.com/Documentation/Splunk/7.3.2/Admin/HowSplunklicensingworks
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