Because wikis are just Git repositories, you can make changes locally and push them to your repository using a Git workflow.
First, download the wiki of your backup. Please open the panel of a backup, click “download wiki” and choose “current” for the latest backup or any of the snapshots available. The download contains the complete wiki repository.
Next, clone the empty wiki of the repository you want to restore into, following the instructions on the GitHub documentation.
Now that you have a local copy of your empty wiki and a local copy from the wiki of your backup, you can simply copy the files from the backup over into the empty wiki and commit them.