100 ohms resistor overheating
How do I fix this?

Add more LEDs in series.

The proper answer is to read the datasheet for the LEDs and design your circuit appropriately. You should calculate the required power dissipation in your resistor.
The LTL-307EE you show in your circuit has a forward voltage of 2V, so your resistor has to drop 8V. Your current at 100 ohms is 80 mA (the LTL-307EE is only rated 20mA and will die soon at 80mA). The power dissipated in the resistor is 640 mW which is too high for a small resistor rated at 125 mW.
So by doing the calculations for your real LED, you might find you need a higher power resistor (e.g. a 10 watt resistor instead of a 1/8th watt resistor). You might choose a resistor with a higher resistance to reduce the current (and potentially extend the life of the LEDs)

Adding more LEDs in series means the resistor has to work less hard.
Using a 5V power supply would be another option.