Step 1: Create a List of Contacts
Create a List of contacts in Create A List to which you’d like to apply the same updates.
Step 2: Access Bulk Apply
From your list, select the Bulk Apply tool.

Step 3: Select Fields to Update
Use the mapping tool to choose which fields you want to change and specify the new values to apply to all contacts in your list.

What else do you need help with?
Overview: Create a ListHow do I map and apply data in Bulk Upload?
How do I perform a Bulk Upload?