Ensure the file is directly in the Fonts folder and not inside a sub-folder.
Here is everything you need to know about downloading and installing Tamil fonts for PicsArt. Why Custom Tamil Fonts Matter Tamil Font Download Picsart
Go to Internal Storage > PicsArt > Fonts . Paste: Drop the font file into this folder. Launch PicsArt: Open the app and start a new project. Apply the Font: Tap on Text and type your Tamil words. Ensure the file is directly in the Fonts