Go to Financial management → Inventory → Costing. Click on application worksheet. Now selec the entry u want to unapply, click on view applied entries and then click on Remove application button.
Now come back to earlier interface and focus on entry which u want to correct and now click on view → select additional entries to apply(see the system to see exact name), or u can just press F11. Now next interface will show u the entries possibly against which u can apply ur entry again. Click on Ok and u r good to go. Now run adjust cost entries to make sure and check that now it is correct application. 