You only need Scrivener and Zotero installed on your computer if you need to create citations and bibliographies.

First get your citation from Zotero (ctrl+shift+A) and paste it into Scrivener (ctrl+v). Select your citation and add a footnote in Scrivener and paste the citation one more time, this time replace the parenthesis with curly brackets.

Compile to RTF (ctrl+alt+e), make sure to select "RTF Document" at the top.

Switch to Zotero and use the "RTF Scan..." function in Zotero's tools menu.

Scan and save and open the resulting RTF-file and all should be working.