While replying, you can use the drop-down arrow mark to choose the 'From' email address as shown in the image below:

If you want to have a common email from which the replies are sent out, you can make use of the App 'Common From email address'
How to change the 'From' email address of a ticket?
While replying, you can use the drop-down arrow mark to choose the 'From' email address as shown in the image below:

If you want to have a common email from which the replies are sent out, you can make use of the App 'Common From email address'