Here's a little trick for changing the "created" field directly from within the TiddlyWiki tiddler editor:
1) View the desired tiddler and invoke the editor (pencil icon)
2) In the "Add new field" field name input, type "created"
3) In the corresponding field value input, enter a date/time value using YYYY0MM0DD0hh0mm0ss0XXX format (e.g., 20200615102030500 = June 15, 2020 at 10:20:30.500am)
4) Press the done button (checkmark icon) to apply the change
Note that this also works for other "hidden" system fields ("creator" and "modifier").
It also works for "modified", but only if you first turn off the automatic timestamp feature (see Sidebar > Tools > Timestamps)
Also note that the timestamp field value is in UDT, so you will need to account for the timezone offset of your location.
enjoy,
-e