You can't change the Fly App, it's the default numbering system. I would try leaving the file with the highest number on the SD Card and then for S&Gs, shoot a couple of photos and see if the new photo's numbers start after that file you left on the card… It's built into the firmware, you are just going to have to try to fool it…
Also, you do realize that if you dump all the photos into a temp directory on your PC (assuming that is what you are doing, you can highlight all those photos and do a Global Renaming.
For example, with the photos copied to that Temp Directory, highlight (CTRL A) all the photos that you took at the "XYZ Park" on 16 Nov 2023. With all the photos highlighted, Right Click and select RENAME, in the selected photo, type in "XYZ Park - 16 Nov 2023" or whatever naming convention you prefer. Then copy those renamed photos over the directory that you want to store them. Each photo will be renamed "XYZ Park - 16 Nov 2023 (1)" and the next one will be a "2" and the then a "3" and so forth…
Give it a try with any old files, whatever the file extension is, it will remain the same (JPG, MP3, RAW, whatever…).
IF you are not sure of what I wrote about renaming all the files in a directory, Google it…