Slots created in various places in VSys can be "recurring", that is, the same slot settings repeated over time. Since recurring slots work by telling VSys the rules for making the slots, those same rules can be used for extending the slots. Slots can be extended individually in the Jobs/slots calendar tool by right-clicking on them and selecting Edit this job slot then Extend it into the future, or you can use the VSys Anywhere Extend Recurring Slots tool.
Put in your filters on Jobs, Locations, etc. Minimum last date and Maximum last date refer to the last date for each recurring slot: only those that end during this date range will be shown. Click Search.
This tool uses "inline" editing: you extend slots by clicking directly on the Extend to date and changing it, optionally adding content to the Comments field. You have to click Save at the bottom for any of your changes to take effect.