You need to reinstall the operating system. If you have another computer available to use, use that to create USB installation media for ubuntu and then you’ll be able to boot ubuntu off the SSD again.
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You can download ubuntu here:
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https://www.ubuntu.com/download
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Use Rufus to burn the downloaded ubuntu ISO onto a flash drive:
You need to reinstall the operating system. If you have another computer available to use, use that to create USB installation media for ubuntu and then you’ll be able to boot ubuntu off the SSD again.