I'm pretty new to Minecraft so this could be an issue where I can't find the control, but it seems that there is no option for me to use an Off-Hand item. There is no control listed for it in settings>keyboard & mouse. It doesn't let me place an object like a torch in the Shield slot on the inventory screen, and hitting F key doesn't do anything.
MCPE-75665
Off-Hand option not available
Resolved
Invalid
0
The off-hand has not been fully implemented into the Bedrock codebase, so for now, this is working as intended. Later on, when the combat update is released (NO DATE), is when you will be able to use the off-hand.