The method for unblocking a Skype contact depends on the way you blocked the contact to begin with. If you blocked a contact and removed him from your contact list, you have to go into Advanced contact settings in Skype for Windows Desktop or search for him on Skype for Modern Windows to find and unblock him. If you blocked a contact but didn't remove him from your contact list, you can unblock him by right-clicking and selecting "Unblock This Person" in Skype for Windows Desktop or selecting the contact, right-clicking anywhere in the page and selecting "unblock" in Skype for Modern Windows.
Unblock Someone on Skype for Windows Desktop
Open the Contacts menu in Skype. Click "Advanced" and choose "Manage Blocked Contacts..." to access blocked contacts settings.
Choose the contact you would like to unblock from the list of blocked contacts. Select the person and click "Unblock this person" and "Save."
Confirm that the contact is unblocked and has returned to your contact list.
Unblock Someone on Skype for Modern Windows
Open Skype and click the "search" icon.
Search Skype for the person you blocked. Click the contact when it appears under people.
Right-click anywhere on the screen and select "unblock" from the options.