I've uploaded an article to ResearchGate, and ResearchGate asks me whether it has been peer reviewed. It hasn't, and I'm wondering whether ResearchGate can get it peer reviewed for me.
Is this possible and if yes how would I do it?
I think I understand your question now. You've uploaded your article to ResearchGate, and ResearchGate asks you whether it has been peer reviewed. It hasn't, and now you're wondering whether ResearchGate can get it peer reviewed for you.
The answer is: it can't. It just wants to mark articles shared on RG that have been peer reviewed elsewhere as such, but it won't have it reviewed for you. To get it reviewed, you would have to submit it to an actual journal.
As far as I know, the answer is no.
Research gate is a site for displaying your work so people can find it. It is not part of the publishing process itself.
Peer-review is what happens after you submit the paper to a journal, before they accept it. I find it strange that the publisher would ask if the paper has been peer-reviewed. Possibly the intended question is whether it has previously been submitted to (and rejected by) another journal, so they can ask to see previous reviews before using up more community time on further ones.
Edit: I can't make up my mind whether the website you are uploading to is Research Gate itself or another journal website. If you mean Research Gate, then the 'is it peer reviewed?' question means 'Has it been accepted for publication?'