See the Explanation for the complete step by step solution.
Explanation:
To add the LinkedIn application as a resource to the Sales and Marketing access package without removing any other resources, you can follow these steps:
Sign in to the Microsoft Entra admin center:
Ensure you have the role of Global Administrator or Identity Governance Administrator.
Navigate to Entitlement Management:
Go to Identity governance > Entitlement management > Access packages1.
Select the Sales and Marketing access package:
Find and select the Sales and Marketing access package to modify it.
Add a new resource:
Within the access package details, select Resources.
Click on + Add resource.
Search for and select the LinkedIn application from the list of available resources.
Configure the resource role:
Assign the appropriate role for the LinkedIn application that users in the Sales and Marketing access package will have.
Review and update the access package:
Ensure that the LinkedIn application has been added as a resource.
Confirm that no other resources have been removed from the access package.
Save the changes:
After reviewing, save the changes to the access package.
Communicate the update:
Notify the relevant users about the addition of the LinkedIn application to their access package.
By following these steps, you will successfully add the LinkedIn application to the Sales and Marketing access package without affecting the other resources.

Reference:
https://docs.microsoft.com/en-us/powershell/module/msonline/set-msoluserlicense?view=azureadps-1.0