While editing a document to change dates from one semester to the next might be the epitome of administrivia, Blackboard, fortunately, has a Date Management tool to help with these updates.
Second, use the Date Management tool in your new course to adjust all dates (such as due dates and availability dates) to match the new semester for your copied or imported content. In most cases, choose the “Use Course Start Date” option, and set the first class session as the new course start date. All due dates will then calculate and update accordingly.
You will find the Date Management too in the Control Panel, under Course Tools.
This short video tutorial provides step-by-step instructions: