Firstly, the only way to do this is from the command line. There is no GUI function to do this.
WARNING: Because you must use the command line, you MUST be careful. It is very easy (too easy) to accidentally expire images/media when entering incorrect dates and/or parameters.
If the backup images went to tape, then you could reset the retention of all backup images on particular media using the command line. If the backup images are on disk, then you will have to be careful, as you will first have to identify exactly which backup images need to have their retention modified.
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Before we continue, can I ask... whether you are comfortable with command line actions/work?
And, I have to ask, do you know how to report/list backup images at the command line?
If not, then then you need to look at the bpimagelist command here:
https://support.symantec.com/en_US/article.DOC6489.html
...or here:
https://support.symantec.com/en_US/article.DOC7673.html
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WARNING: It is very important that you first determine which backup images you need to modify the retention of. My advice is to not begin to modify/reset/change/update the expiration date of backup images until you have first clearly and concisely identified the images that need to be modified/updated.
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It becomes more complex if the images were or are being processed by SLPs, and if multiple stages in SLPs exist, and thus multiple copies exist.
Do you have any idea how many backup images we are talking about?
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How ciritical is it that the backup images are not lost? i.e. is there a serious financial penalty, or even risk of prosecution if the backup images expire too early? If so... you may be best placed calling in Symantec Professional Services, or a good reseller with super tech skills, to help you.
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(FYI - I have deliberately NOT told you how to reset the image expiration dates, because we firstly need to understand the scale, and complexity, and attached risks for this situation/problem.)
