How to Reverse a Journal Entry in Acumatica:

In Acumatica, you can reverse a GL Batch with a simple click.
Pull up the Entry that you wish to reverse in the Journal Transaction window.

Click on Actions->Reverse Batch

This will bring up a new entry, marked as a Reversing Entry, containing the original details with the debits and credits reversed. The Original Batch Number is also noted on the reversing entry, so that you can drill back to the original entry.
The new entry will be in a Balanced Status. You must Release the batch to post it.
Note that the original entry remains unchanged but it does have a reference to the reversing batch.
Clicking on the Reversing Batches link will show the GL Reversing Batches report for this batch number.
If you attempt to reverse a batch that did not original in GL, the system will warn you. You can still proceed with the reversal, but the transaction in the originating module will not be affected. If you wish to reverse the originating transaction, you should do so in the originating module.