You will be able to find a range of free and paid online training via Google. You can find some recommended resources below.
Free YouTube videos by INTERACT EU project
The INTERACT EU project produced 2 YouTube playlists with 17 short training videos on translation and post-editing for volunteer translators: https://www.youtube.com/channel/UCRbg0k_1W8KU1xDFqZjDZtg/featured
The videos are designed for volunteer translators in humanitarian crises, but they are a good introduction for any volunteer translators, and Cochrane translators tested the training.
TAUS e-learning
TAUS is an independent organization that shares knowledge, metrics and data to support people and businesses doing translations and related activities. TAUS offers a range of resources and training, including online courses on post-editing and quality management of translations: https://elearning.taus.net/course/index.php. These courses come with a fee.
Free Portuguese videos by Cochrane Brazil
Cochrane Brazil produced 7 training videos for Portuguese Cochrane translators, which are freely available on YouTube: https://www.youtube.com/watch?v=Z6gM2YbI2fc&list=PLE7PSOAHHyt4pgkgj9dPg4FvTqAqbBfB4