There is an “Upload / Submit” tab that serves as a control center for such operations. You can find it to the right from the “Directory tree” tab. Activate it by clicking it, then select a group of files and you will see their status for every agency:
Submission is performed automatically by M+ as soon as possible, you cannot trigger it manually because there is no need for that. If it doesn’t happen then probably something is wrong. It could be caused by lack of submissions left for this agency, or by some internal agency error, or by changes on the agency that require our intervention. If the files have appeared at the agency website, you have enough submissions but the submission didn’t happen within 2 hours - please contact our support.