In today's uncertain business setting, the intensity of rivalry amongst service firms requires a high level of quality and adaptability from service staff to fulfill increasing customer needs and wants. Indeed, every individual's ability to adjust to changing demands is vital for management to promote within their companies. The present study proposes and tests a novel self-regulatory adapting mechanism to examine the conditions within which service staff might activate their ambidextrous behavior which can be beneficial for their proactive service performance. Based on Trait Activation theory (TAT), Individual Adaptability Theory, and Job demands-resources theory, we analyze the direct and mediating effects of certain personal characteristics (Proactive Personality) and initiatives (Playful work design and Uncertainty adaptability) to activate the ambidextrous mode of employees toward higher proactive service performance. To test our hypotheses, we collected survey data from 368 frontline banking employees in all three regions of Vietnam. Practically, the results and recommendations from this study will assist in the hands-on management and motivation of service representatives toward better proactive performance.