Hi there, drm2.
If you're to adjust the profit and loss or transaction reports, then you can edit the transactions and make sure to select the correct categories.
For missing transactions, you'll have to re-create them. However, if you're trying to amend the forms, you will have to do it manually to the HMRC.
You can also check these articles for reference:
Should you have other questions or concerns, feel free to leave a comment on this thread. Thanks.