How to associate a supervisor with an employee

I have inherited a Form and need to assign a certain supervisor to a list of employees into this form.  I have 0 coding experience and do not know anything beyond the extremely basic bits of creating a form.  I have the list of employees and list of supervisors as a text drop down but I would like to associate the employee's name with their supervisor to auto populate.  How can I do this? Thank you for your patience and understanding!