Hi @nachi,
upgrade from 7.3.0 to 9.x is a long path because they are a very different products and you have to change the python version,
so at first you have to migrate at 8.0.x or 8.1.x, following the steps at https://docs.splunk.com/Documentation/Splunk/8.2.1/Installation/HowtoupgradeSplunk
then at 8.2.x https://docs.splunk.com/Documentation/Splunk/9.1.0/Installation/HowtoupgradeSplunk
then at 9.0 or 9.1
and at least at 9.2 as described at https://docs.splunk.com/Documentation/Splunk/9.2.0/Installation/HowtoupgradeSplunk
Special attention must be used in App migration because python changed and the old apps could not be compatible with the new version; use the Upgrade readiness app (https://splunkbase.splunk.com/app/5483) to check your apps followinf the documentation at https://docs.splunk.com/Documentation/Splunk/latest/UpgradeReadiness/About?_gl=1*fwtqsv*_ga*MzU3MjIz...
For the apps from Splunkbase, find the new versions compatible with the latest Splunk version.
Ciao.
Giuseppe