How do I use digital pin on sensor to analog on arduino uno
PWM stands for Puls Width Modulation and is only available when the Digital Pin is in OUTPUT mode.

And YES, you can connect the flame sensor's D0 to any digital pin on the Arduino.

And yes it is possible to connect the flame sensor's D0 to a analog pin, but why not use the A0 from the flame sensor and connect it toi a analog pin on the Arduino?