Step 1: Sign into Office 365 admin portal via https://portal.office.com
Step 2: Click on Admin icon and navigate to Users > Active users.
Step 3: Select an user from the list of users.
Step 4: Switch to Licenses and Apps and scroll down to the Apps section.
Step 5: Check/uncheck the checkbox respective to the App to enable or disable it.
Step 6: Click on Save changes.