Warning: Install folder still exists and should be deleted for security reasons!

my opencart version 3.0.3.8 ( Warning: Install folder still exists and should be deleted for security reasons!)

plz help me

This means the /install/ directory still exists on your server. Someone could use that to re-install OpenCart, which is why it's a security risk. You can either rename that folder to something else, or delete it entirely (since you shouldn't need it again).

I still wondering why the Core team hasn't come with the Function to delete these after a sucess install/upgrade...