Canon EOS REBEL T7i Instruction Manual page 124

S Selecting the AF Area and AF Point
Selecting the AF Area Selection Mode
In the <8: x> and <v: Xc> modes, you cannot select the AF

area. Single-point AF (fixed at center) is applied for shooting.
In Basic Zone modes, if you change the shooting mode or set the power

switch to <2>, the setting will revert to the default.
In Creative Zone modes, if you set [6: AF area selection method] under
[54: Custom Functions(C.Fn)] to [1:S9Main Dial], you can select the
AF area selection mode by pressing the <S> or <B> button, then turning
the <6> dial (p.393).
124
Press the <S> or <B> button
1
.
( )
9
Look through the viewfinder and

press the <S> or <B> button.
Press the <B> button.
2
Each time you press the <B>

button, the AF area selection mode
changes.