You will be able to find a range of free and paid for 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 is an independent organization which 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