To move workitems from one sprint to another , all you have to do is follow the below steps

Step 1: Go to the Past Sprint as shown

Step 2:  Select the Bugs or any workitems, then right click near the gap between Order and Title

Step 3:  When you right click, you can see options like shown below

Step 4: Click on “Move to Iteration” and then choose the Current iteration

Step 5: Once you have selected the new iteration, you can see all the work items in the new iteration