Canon EOS 250D Advanced User's Manual page 267

[Manual reset]: When you wish to reset the file numbering to 0001
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or to start from file number 0001 in a new folder.
When you reset the file numbering manually, a new folder is created
automatically and the file numbering of images saved to that folder
starts from 0001.
This is useful, for example, if you want to use different folders for the
images taken yesterday and the ones taken today. After the manual
reset, the file numbering returns to continuous or auto reset. (There will
be no manual reset confirmation dialog.)
If the file number in folder 999 reaches 9999, shooting will not be possible
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even if the card still has storage capacity. The LCD monitor will display a
message telling you to replace the card. Replace it with a new card.
For both JPEG and RAW images, the file name will start with "IMG_". Movie
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file names will start with "MVI_". The extension will be ".JPG" for JPEG
images, ".CR3" for RAW images, and ".MP4" for movies.
In [File numbering] under the [5] tab,
select [Manual reset], then select [OK] on
the confirmation dialog.
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