The 'Un-Clear Journals' module allows you to un-clear a journal entry that has been posted as cleared.

Select the entries that you wish to un-clear and select the un-clear button at the bottom of the page. The module also shows you the total amount of posted journal entries as well as the total amount of what you select to un-clear

Be careful, however, as any changes you make from clearing and unclearing journals will affect your bank statement.