Are you one of the many LinkedIn users with more than one profile? For instance, you may have created a second account because you no longer have access to your old signup email address.
How do you go about merging the two (or more) accounts?
Unfortunately, there's no automated way of handling this and LinkedIn can only help if both/all of your accounts have more than 10 connections
If you have 10 or less connections on one of your profiles, you're on your own. You basically have to manually reconnect with your old contacts on your new profile. You can request an archive of your data from LinkedIn but it's hardly worth it.
If you can't log in to the old profile to shut in down, you'll have to contact LinkedIn and ask them to do it.
More than 10 connections
If you have many connections, LinkedIn will do the transfer for you and close the old account. However, there are several things that LinkedIn can't transfer from one profile to another: Recommendations, work experience etc. So consider carefully which profile you choose to axe.
You can find LinkedIn's detailed description here: https://help.linkedin.com/app/answers/detail/a_id/1275/~/duplicate-accounts