You can easily turn off Dark Mode on Snapchat from your Android and iPhone by following these steps:
First, you have to update your Snapchat application to the latest version.
Open the Snapchat app and then choose your profile picture.
From the top-left corner, click on the Settings icon.
Explore to the bottom of the page and find App Appearance in the options of my account list.
Tap on App Appearance
Now select the Always Light to turn off Dark Mode.