How to change E0 to E1 on Marlin 1.1? I have the same problem as this person but I don't have those lines in my RAMPS.h file as seen here.

I've recently burnt my potentiometer on E0 so the motor isn't working properly anymore. I want to use it on E1 instead. If you have any better idea how to fix this instead of changing code in firmware, feel free to share.
Another posting already discusses how you can change the pins to use spare stepper controllers for broken controllers by changing the pin layout. Assuming you are using a RAMPS board and using Marlin firmware, you should look at the pins_RAMPS.h file.

This file requires changes to address E1 to E0 and vice versa, please edit the file so that:

#define E0_STEP_PIN        26
#define E0_DIR_PIN         28
#define E0_ENABLE_PIN      24
#define E0_CS_PIN          42


is changed to:

#define E0_STEP_PIN        36
#define E0_DIR_PIN         34
#define E0_ENABLE_PIN      30
#define E0_CS_PIN          44


and also change:

#define E1_STEP_PIN        36
#define E1_DIR_PIN         34
#define E1_ENABLE_PIN      30
#define E1_CS_PIN          44


to:

#define E1_STEP_PIN        26
#define E1_DIR_PIN         28
#define E1_ENABLE_PIN      24
#define E1_CS_PIN          42


When the file is changed an saved, build and upload code to your board and plug the connector of the E0 stepper into the E1 header.