You are the global admin of an organization with a Microsoft 365 subscription. Two days ago, you created retention labels and published the labels to Microsoft Exchange Online mailboxes. You notice that the labels are not appearing. You need to make them available for manual assignment. What should you do?

Answer options:

A.From the Security & Compliance admin center, Recreate the labels.
B.From Exchange Online PowerShell, run Start-ManagedFolderAssistant
C.From the Security & Compliance admin center, Auto-apply the labels.
D.From the Security & Compliance admin center, create a label policy.

Correct Answer: B 
You can check the status of retention labels pushed to Exchange by running these commands connected to Exchange Online Powershell: 

The result will show when the system last processed your mailbox. If it has not happened since the time you created the policy, the labels are not going to appear. To force processing, run Start-ManagedFolderAssistant -Identity «user».
Option A is incorrect. Deleting and recreating the labels will not enforce the processing of your mailboxes.
Option C is incorrect. This feature has the ability to apply labels automatically to content that matches specified conditions.
Option D is incorrect. You can use a retention policy to assign the same retention settings for content at a site or mailbox level (retention label assigns retention settings at an item level - folder, document, email)
Reference: 
To know more about creating retention labels, please refer to the link below: 

https://docs.microsoft.com/en-us/microsoft-365/compliance/create-apply-retention-labels?view=o365-worldwide