Elaborating on Bernard's post, the typical 555 PWM circuit duty-cycle is normally controlled by a pot.
If you want the duty-cycle controlled by an input voltage than a different circuit is likely more appropriate.
Another approach using Arduino / ATTINY85. Consider this for future designs.
Gives good timing accuracy (2% error on ATTINY, << 1% error for Arduino NANO
or UNO boards)
mBlock using block programming generates the Arduino / ATTINY85 code. You
drag and drop blocks, config, and mBlock generates the code you see in right
hand window and with tool upload to Arduino. ATTINY85 takes a couple of
extra steps to program it.