you need to view the files and folders inside the app. i dont have a mac, but from explanation on the internet i see that you can do it by pressing on the Finder option, and then look for the app in the location where you saved it.
after entering the folder of the chapter2, drag all the files from there into the folder of chapter1 while pressing on the Option key- this way you will be able to choose the merge option for the files.
you may also be able to do it by pressing on the Option key and just drag the chapter2 app onto the chapter1 app and press on the merge option. i think that it worked for players too, so try it first since it seems easier. you will know that the merging succeeded if after starting the game you see the version of your latest merged chapter in the main manu.
consider joining the discord server of the game, its easier and faster to answer there
