I have verified my identity with Companies House. What do I do with the personal code?

Send it to us so we can include it in the incorporation filing. The code belongs to you, not to a company, and you reuse it for every UK role you hold, including a later director appointment. Share it only with people you trust to file for you, as you would a tax reference.

Source: Verifying your identity for Companies House, Companies House, GOV.UK