If you run 12 period accounting and have a transaction posted into period 13, this will cause an issue as your reports will only be available up to period 12 and will exclude the transaction in period 13.
The best way to approach correcting this is via the use of the corrections module.
Log onto Dimensions as a user with access to corrections
Use the enquiry screen to load up the transaction list that holds the transaction in question
Right-click the transaction and select Correct
On the corrections screen, click Edit
Select the new period and year for the transactions (ensure that this is an open period and year).
You can then reverse the transaction if you wish to do so.
Note: If you do not have the corrections module as part of your contract for Dimensions, the only way to move the transaction is via the use of the Datachecker application. Datachecker is a separate application that can be used for a number of high level accounting functions and would usually only be available to senior members of an accounting team or an IT department. Therefore, if you do not have corrections as part of your contract, please consult either senior members of your accounts department, or your IT team, to request that the transaction is moved.