Canon EOS REBEL T7i Instruction Manual page 206

D Using the Built-in Flash
3 Flash Exposure CompensationN
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.
 When you press the shutter button halfway, the <y> icon will
appear in the viewfinder.
After taking the picture, cancel the flash exposure

compensation by setting it back to 0.
If [z2: Auto Lighting Optimizer] (p.169) is set to any setting other than

[Disable], the image may still look bright even if a decreased flash
exposure compensation is set.
If flash exposure compensation is set with an external Speedlite (sold

separately, p.209), you cannot set the flash exposure compensation with
the camera (Quick Control or External flash function settings). If it is set
with both the camera and external Speedlite, the Speedlite's setting
overrides the camera's.
206
Select [Flash control].
1
Under the [z2] tab, select [Flash

control], then press <0>.
Select [Built-in flash settings].
2
Select [2exp. comp.].
3
Set the compensation amount.
4
If the exposure is too dark, press the

<Z> key (for increased exposure).
If the exposure is too bright, press the
<Y> key (for decreased exposure).