The proceedings are to be submitted directly to the AO4ELT website. For that, you need to do a resubmission. Login to your account, and start a new submission (submit a paper) to attach your proceeding.
The link is here: https://ao4elt7.sciencesconf.org/user/submissions
At the first step, choose Type -> Proceeding (this is important to get a proper number that will be used for the DOI later)
At the 3rd step, upload your PDF
Proceedings will be reviewed by the SOC, to ensure the homogeneity of the contributions.
Feel free to contact us if you have any issues or any questions.