For public repositories, the fix PR will be opened by Snyk-bot.
For private Github repositories, they require collaborator permissions to open fix PRs. When automatic pull requests are enabled for private repositories, Snyk selects randomly from the list of users with the right Github permissions and opens the PR on that user's behalf.
You can control which user creates Fix PR's in Github by following this article: Integrating GitHub to Snyk via a Personal Access Token