This is indeed not a feature of Jira. There was a feature request for this raised a few years ago, but it was decided that it won't be implemented:
You will need to manually upload the same avatar on both applications.
Let us know if you have any questions about this.
One more thing, there are a few more workarounds on this page:
You may be able to use something such as Gravatars to sync across both apps, so please feel free to give that a try.
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