During neurofeedback (NFB) user training, participants learn to control the feedback associated with specific components of their brain activity, also called neuromarkers, to improve the cognitive abilities related to these neuromarkers, such as attention and mental workload. The recent development of methods to record the activity of several people's brains simultaneously opens up the study of neuromarkers related to social interactions, computed from inter-brain synchrony (IBS). Here, we review the previous articles that trained participants to control electroencephalographic neuromarkers computed from inter-brain metrics. The topic remains relatively unexplored as we only identified seven articles in the literature. We specifically studied the characteristics of the user's training, i.e., instruction, task and feedback, and the neuromarkers used to provide feedback. The reported results are promising as four studies including subjective measures of interaction report higher interaction and relationship scores with higher IBS during NFB training. Finally, we draw guidelines, identify open challenges, and suggests recommendations for future studies on this topic.