Hi @MC -- Welcome to the Atlassian Community!
No, you cannot reset the issue key starting point. The keys are assigned by the project, starting at 1. To "reset" the count you would create a new project. I recommend leaving them alone as this is just a tracking identifier.
Now for a suggestion: don't delete issues from Jira Cloud. There is no "undo" or "recycle bin" to reclaim items. Consider instead adding an indicator for "abandoned" items, such as with a custom field or a label. You may easily hide these items, and you can find them if needed in the future.
Catch up with Atlassian Product Managers in our 2020 Demo Den round-up! From Advanced Roadmaps to Code in Jira to Next-Gen Workflows, check out the videos below to help up-level your work in the new ...
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