@terrydelia not sure what you refer to as the back cover. Let us know if this is the cover where the LCD is housed, or where the keyboard is, or even the bottom cover. Officially, these parts are not available but you can get them most likely at places like ebay etc.
To replace those covers/parts etc. download the service manual for your computer [https://dl.dell.com/content/manual51988634-inspiron-13-5310-service-manual.pdf?language=en-us|from here]