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You need to use a work account as a bridge:
- Sign into Learn with your old personal email account
- Link a work account to your old Learn profile https://learn.microsoft.com/training/support/learn-profile-manage#add-login-accounts-to-your-learn-profile
- Sign into Learn with a work account
- Remove the old personal email account from the Learn profile
- Link and merge your new personal account to your Learn profile https://learn.microsoft.com/training/support/faq?pivots=profile#can-i-merge-two-profiles-of-mine-into-one
- Optionally, sign into Learn with the new personal account and remove the work account