Up-vote the suggestion to solve this issue! As it is now, you can only create a new sprint from the backlogg and then move it one step at a time to where you want it.
Up-vote here:
Recommended Learning For You
Level up your skills with Atlassian learning
Learning Path
Become an effective Jira admin
Manage global settings and shared configurations called schemes to achieve goals more quickly.
Streamline Jira administration with effective governance
Improve how you administer and maintain Jira and minimize clutter for users and administrators.
Learning Path
Become an effective Jira software project admin
Set up software projects and configure tools and agile boards to meet your team's needs.