if you are using the ‘set field’ behaviour, should be as simple as you have mentioned here where your forumla is
Text field 1
Text field 2
although you may want to include a ‘Special – New Line’ to the 2 text fields dont just append into one line
also consider what your max characters are in these 2 fields so that your destination field is set to allow both maximum lengths.
But again, if you can’t see it, raise in the support ticket where you can attach your form and give details of where these 3 fields are on the form and how the script to ‘add’ is invoked.