Using a formula to append strings

[JohnDoe]

Is there a way to append data in a field? Let's say I have a long text field called "Campaigns" which will contain the different campaigns that a customer have agreed to through our emails. 

Is there a way to preserve the previous text and basically add the new text to the field? 

[TheTimeSavingCo · Accepted solution]

Yeap, I would use an automation for that and it'd look something like this:

Link to base