Canon EOS 70DN Basic Instruction Manual page 376

Using Wireless FlashN
Creative Wireless Flash Shooting
Flash exposure compensation
When [Flash mode] is set to [E-TTL II], flash exposure
compensation can be set. The flash exposure compensation
settings that can be set (see below) will differ depending on the
[Wireless func.] and [Firing group] settings.
FE lock
If [Flash mode] is set to [E-TTL II], you can press the <A> button to
perform FE lock (p.192).
212
Flash exposure compensation
The flash exposure compensation is
applied to the built-in flash and all the
external Speedlites.
2 exp. comp.
The flash exposure compensation is
applied to the built-in flash.
1 exp. comp.
The flash exposure compensation is
applied to all the external Speedlites.