someone else has accepted authorship of some works that are really mine, as I can prove, and I would like to retrieve them and add them to my list, but I don't know how to do it. I attach a screenshot of the person and my work.
This is a frequent problem in ResearchGate in case of similar names. See "A researcher has wrongly claimed co-authorship of my publication" in https://explore.researchgate.net/display/support/Authorship for instructions how to correct this. But unlike this help page suggests, most probably it was not the other author herself who wrongly claimed authorship, but ResearchGate's automatic algorithm wrongly identified another researcher as the author and assigned your publication to her profile.
The above link is helpful for your claim. Another way I suggested is to contact your co-author and edit your publication and remove your old name and to add your exact name.
Re-upload the paper to your own RG account. When you do so, the system will ask you if the initial paper is yours, reply yes. It will be removed and assigned to you.