To merge any two accounts, follow the procedure outlined on the "User Merge" help page:
I accidentally created two accounts; how do I merge them?
If you have two accounts that you would like to join together, please sign into either account, visit the contact form and select ‘I need to merge user profiles’. After you contact us, the Stack Exchange Team will reach out to verify that you own both accounts. If we can confirm your ownership, we will initiate a merge.
If you can't remember how to log in, go here and enter the email address you used to create the account you are trying to sign into.
If you're into URL modification, you can just go directly to
https://$site/help/merging-accounts. For example, https://stackoverflow.com/help/merging-accounts, https://english.stackexchange.com/help/merging-accounts, and so on.
Stack Overflow for Teams members
If you are a member of a Stack Overflow Team, to expedite your account merge request, do not use the normal contact form above - instead, open a ticket. (You do not need to leave any Teams you're a member of.)