Canon EOS 90D Advanced User's Manual page 188

Wireless Flash Photography Using Optical Transmission
Advanced Wireless Flash Photography
 Flash exposure compensation
Available when [Flash mode] is set to [E-TTL II]. Note that the setting items
available for fl ash exposure compensation (see below) vary depending on
[Wireless func.] and [Firing group] setting details.
FE lock

You can lock the fl ash exposure (FE Lock, = 167) by pressing the < A >
button.
188
Flash exposure compensation
The same amount of fl ash exposure

compensation is set for the built-in fl ash
and all external Speedlites.
2 Flash exposure compensation
Set fl ash exposure compensation for the

sender.
1 Flash exposure compensation
The same amount of fl ash exposure

compensation is set for all receivers.