Obtain the schematic of the LED flasher circuit you want to stop the LEDs from blinking too fast. Locate the resistors on the circuit schematic. Look for any notes on the schematic that may give you a clue as to what resistors control the blinking rate. Write down the values of the resistors that are on the schematic.
Open up the LED flasher circuit so that you can see the components that are in the flasher. Locate the resistors on the printed circuit board. Read the values written on the resistors and match them to the resistors on the schematic.
Attach a variable resistor to the right and left leads of one of the resistors on the circuit board. Turn on the flasher. Adjust the value of the variable resistor with a small screwdriver and observe whether or not the LED blinking rate slows down with the change in resistance. Remove the variable resistor and attach it to the left and right leads of another resistor. Continue in this fashion until you locate the resistor that controls the LED blinking rate.