A good place to start is to print a print quality test page or self test report. The print should show the colors in either bars or typing, the colors should be clear and sharply defined. One or more colors may be printing offset compared to the other colors and that offset can make the image look blurry or even a double print.
HP has a tool that you can download, found on this page (https://support.hp.com/us-en/product/hp-laserjet-pro-cm1415-color-multifunction-printer-series/4089171/document/c04927206). This tool is supposed to fix scanning and other problems.
If the tool does not fix the problem, remove the toner cartridges and drums and inspect the laser aperture for dust. Use a clean lint free cloth to remove dust, do not use canned air as that will just blow dust to places hard to clean. A laser vacuum or finely filtered vacuum can be used, house hold vacuum cleaners are not suitable because it will suck up the toner and blow it out the exhaust.