If you have an underperforming employee reporting to you. How do you address the situation?

First i would review their performance and where the gaps are then i would communicate the issue to them to try to identify the problem wether it's a lack of professional skill, understanding of the tasks or a personal problem.

If the problem is lack of professional skills or understanding of the tasks, i would review their set KPI, remodulate it that performance would be increased while avoiding stressing the employee, in addition i would arrange or suggest trainings based on the analysis depending on the company's policy