You don’t need to do anything. You just follow his rulings and if there is an issue that comes up you refer to his opinions. You can find his opinions on the website Sistani.org
If several experts tell you sayed Sistani is the most knowledgeable, you can take their word. Today sayed Sistani is the most followed marji, therefore you can follow the suggestion of the experts and follow him. If you choose to do your own research you can.