I think you would be better off moving your entire existing 6.3.2 instance to the new server and then upgrading to 7.2.6 afterwards. See Migrate a Splunk Enterprise instance, and then you would do a normal upgrade as described in How to upgrade Splunk Enterprise. You will have to upgrade from 6.3.2 to 6.6.x, and then to 7.2.6.
Or you could upgrade from 6.3.2 to 7.0.x, and then to 8.0.2, if you want the latest software. See the 8.0.2 version of How to upgrade Splunk Enterprise for more information about that.
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