Do either case, then repeat.
Look at top face – you have one of 3 cases: guide to solve rubik 39-s cube pdf
THE SIMPLEST WAY TO SOLVE THE RUBIK'S CUBE A Beginner's Method – Layer by Layer Do either case, then repeat
Find if any face is already solved except top layer. Hold solved face at back. Do either case
Do R U' R U R U R U' R' U' R2 Then check – may need once more.
(horizontal): F R U R' U' F'
(top-left corner): F U R U' R' F'