If you need to unlink the person, click on the "Relink Record" highlighted below.
Click on "Unlink" the contact
Your contact will be unlinked automatically
If the LinkedIn contact is not connected to the CRM and you know it’s there and you want to connect it manually.
Go to your target profile on LinkedIn and click on the "Link record" option
A pop-up will appear, where you can select which CRM record you’d like to link the LinkedIn profile to.
Now select the correct person to be linked to the CRM record and click on "Link contact to this record".
Learn more about how to map LinkedIn URLs for your contacts here.