The development of pedagogies that can provide alternatives to traditional approaches is becoming increasingly important as a means of enhancing the attractiveness of training courses, appealing to new types of learners and designing learning systems that help to develop multidisciplinary skills. In this context, the JEN.lab project aims to offer innovative perspectives for learning based on the design of digital epistemic games (JENs in French). The research effort presented in this paper is part of the JEN.lab project. We aim to study problems related to the modelling and design of digital epistemic games. We propose a co-design process and an assistant tool supporting this process to guide teachers in designing digital epistemic games called ADDEGames (Assistance Design tool for Digital Epistemic Games). Our approach is based on: (i) the learners and the situation that emerges when they play the game, rather than the device used to play; and (ii) the teachers who want to manage a game-based learning situation. The iterative and participative development process and acceptance test using an agile approach are presented.