Grammarly can help you, but I recommend wag ka nalang gumamit ng app.
Mas maganda gawin mo, magbasa ka ng magbasa, it can be books(with stories) or news papers, etc basta mag basa ka lang, kung alin interesting sayo.
Then do some writings, subukan mo ding sumulat. Ganyan lang, you can do it on your own, kahit di na kailangan ng app.
Yun lang ^^