Look up the GetNthRecord function in FileMaker help.
As long as your records are always correctly sorted and you can use an unstored calculation for this:
GetNthRecord (Events::EventEnd ; get ( RecordNumber ) - 1 )
In some circumstances, (experiment and see), you can use the "value from last visited record" to auto-enter the value. That option enables you to use a stored, indexed field (needed in some cases and faster for searches and sorts in others) as well as allowing you to directly edit the value in the field should you ever need to.
Final note: There are much better ways to move data from one place to another than copy and paste. Copy and paste wipe out anything that the user has copied to the clipboard and also will silently fail to work if the field they copy from or paste to is not present on the current layout. Thus, scripts that use copy/paste not only irritate/confuse the user by mysteriously changing the clipboard contents, a future edit of a layout can result in a script that then mysteriously fails to work as expected. You can, instead, use set variable to copy the value and Set field to "paste" the value from the variable to the field and avoid both issues.