Navigate to Settings -> Email Campaign Settings -> Footer Setting.
Provide the company details on the mandatory fields and click 'update'. This will automatically get updated on the footer of the emails which you create.
Including company details from the editor:
In the campaign Design tab, the company details can be added to the footer block by using Merge Tags option. If they are not included manually, the default footer settings will be included as shown below. This default text can also be customised using the template editor.
You will not be able to send the campaign if the footer settings are not set. A warning will be shown on the Review tab under the design issues. After updating your company details, you can edit the same before sending a campaign using the below Edit option.
Note: This setting is global for all the campaigns you create and this can be edited at any time.