If you took out a loan prior to your mission, you will go into repayment while on your mission. Please contact your lender directly to notify them of your plans and to ask about repayment options. Most lenders will happily work with you to make arrangements for a minimal or no monthly repayment option while you are away.
Your federal loan records are housed in the National Student Loan Data System (NSLDS), including contact information for your lender (who you pay back ). Log in to nslds.ed.gov with your FSA ID.