You need to use ireport to fix this

Open Ireport and open your invoiceitemsA5.jrxml template from your OpenVpms report folder.

when it opens you should see the image in workspace.png attached to this post

Select the field I have in the image. it should have the expression $F{target.startTime}

Look to the right of the workspace for the properties (see workspace2.png)

and find the property 'patten' it is probably set to MM/dd/YY, what you want is dd/MM/YYYY (long version) or dd/MM/YY  (short version)

save the file.

Go it OpenVPMS as an administrator - open administration - open templates and find the Invoice items template select CHOOSE FILE and navigate to the report folder where you just save teh jrxml file, find it and select it.  then press OK.

This will upload the report over the old version that had the incorrect date