To set a Price Alert on CoinGecko.com, simply click on the "alarm" button on the coin you wish to set the alert of:


A price alert feature will pop up for you to set the price alert, you may either set a custom number or quickly choose a set percentage:


You will receive a price notification once the price hits the level in which you have set.

For a detailed tutorial, please read How to Set Up the Price Alert Function on CoinGecko?