There are several ways to heat tortillas.
Stovetop: individually heat tortilla on a skillet over medium heat 30 seconds on each side back and forth until desired temperature.
Oven: Lay tortilla on flat baking rack (not overlapping) and cook at 350 degrees for 15-20 minutes.
Open Flame (grill/gas): Place tortilla directly overtop a flame on a grill or gas stove over low to medium heat. Cook for up to 30 seconds while rotating. Prevent excessive burning and fire by watching the tortilla carefully.
Wrap warm tortilla in a cloth to keep warm.