Adjusting Created/Start Date of Issues

[Kat]

Note: I am not using Project. I'm using Jira Core.

I am a project admin that was given control over a list of 60 issues that were created months ago but some started within the last 30 days and others haven't even started yet. I am trying to utilize the charts Jira develops, but since the issues were so long ago, the charts reflect issues taking month. Is there a way to backdate issues when since their start dates vary so much? Or do I need to create a whole new project and manually input each issue as they start?