Canon EOS 250D Advanced User's Manual page 171

Flash Exposure Compensation
Set the flash exposure compensation if the brightness of the subject does
not come out as desired (so you want to adjust the flash output) in flash
photography. You can set the flash exposure compensation up to ±2 stops
in 1/3-stop increments.
1
Select [Flash control].
Under the [z] tab, select [Flash
z
control], then press <0>.
2
Select [Built-in flash settings].
3
Select [2exp. comp.].
4
Set the compensation amount.
If the exposure is too dark, press the
z
<Z> key (for increased exposure).
If the exposure is too bright, press the
<Y> key (for decreased exposure).
When you press the shutter button
B
halfway, the <y> icon will appear in
the viewfinder.
After taking the picture, cancel the
z
flash exposure compensation by
setting it back to 0.
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