In that case then the the best and most accurate answer/guidance is likely this one (click the link for the full info):
There are some hoops to jump through, but you would not be starting from scratch.
Regarding pay, there are only a couple companies operating US Flag tankers, so not sure if you’ll get a reply from anyone who works for one. For reference though, if you wanted to work verrrrrry long trips with little to no time off, the posted C/E salary for a Military Sealift Command tanker is $223,408 as of July 2021 (last page). Though while they occasionally post for 1st A/E jobs I don’t believe they ever hire C/E directly from outside the organization.