I understand that you are trying to re-enroll your printer into the Instant Ink program. I would like to help.
For the most part, you do have to treat the printer as a "New" printer. You can log into your Instant Ink account and select "Enroll Another Printer". You can then pick a plan. On the next screen/step, you will have an option to either add a new printer via the printers claim code, or select the printer that is already on your HP Connected/Instant Ink account.
You then have to just verify the shipping and billing information. Refer to this document to know how to enroll in Instant Ink.
Let me know how this goes.
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