Before you can decrease stress for your Digimon that had been stressed out, you must have access to the Back Item Shop which can be unlocked later on in the game. Anyway, once you have access to it.

Buy some Digi-farms, remodel them by increasing the farm's size and exp gain. This will allow you to add more digimon, farm goods, and level up some digimon in your farms. Try to max out all the ...