How can I copy files and change owner?

I have this step in my config:

    image: rust
    group: deploy
      - cargo doc
      - cp target/doc/* -R /deploy-docs/
      - /var/www/docs/stonedguy-ci:/deploy-docs/

But when the files are copied there, they have root as owner and so I have problems with it because files there must not have root rights. How can I change the user to my host-machine’s nginx user during deployment?