help with 555 timer to dim led driver
You should tie the /RESET pin to Vcc. If you have a CMOS type this can keep it from working. 

Pin 5 may be optionally connected to ground through a 10nF capacitor, but leaving the pin open will not keep the circuit form working. 

Your power supply needs two connections (only one is shown connected in the above schematic), but it should not be as high as 8.4V. The module specifies no higher than 6V. I suggest an LM7805 regulator to give you 5.0V if you don't have such a supply available. It's not clear whether excessive input voltage would damage the module, so I would avoid it. 

The circuit you show will allow the average light to be varied from mostly on to around half brightness. If you want more range than that, it's better to use a couple diodes with the circuit. If you have the CMOS type there is an even better way to connect it- leaving pin 7 open and using the output. You can test the 555 output with an LED and resistor to GND- it should vary the brightness- before connecting it to the module.