Formerly Incarcerated Reenter Society Transformed Safely Transitioning Every Person Act or the FIRST STEP Act This bill amends various provisions of law and sets forth new provisions: to require the Department of Justice to establish and the Bureau of Prisons (BOP) to implement a risk and needs assessment system to assess prisoner recidivism risk; guide housing, grouping, and program assignments; and incentivize and reward participation in and completion of recidivism reduction programs and productive activities; to modify the computation of good time credit; to allow federal correctional officers to securely store and carry concealed firearms on BOP premises outside the security perimeter of a prison; to limit the use of restraints on federal prisoners who are pregnant or in postpartum recovery; to require a prisoner to be placed at a facility not more than 500 driving miles away from the prisoner's primary residence; to require low-risk prisoners to be placed on home confinement for the maximum amount of time permitted; to reauthorize through FY2022 and modify eligibility for an elderly offender early release pilot program; to require the BOP to help prisoners obtain identification documents prior to release, to incorporate de-escalation procedures into training programs, and to make tampons and sanitary napkins available free of charge; to repeal the National Institute of Corrections; to authorize Federal Prison Industries to sell products to additional markets; to require probation and pretrial services officers to perform court-directed supervision of sex offenders conditionally released from civil commitment; to require auditors who monitor compliance with national prison rape standards be certified; and to require the BOP to establish pilot programs on youth mentorship and service to abandoned, rescued, or vulnerable animals.