To use peek and fire option that allow you to activate the tilt mode, please follow the below process.
Click [Setting] -> [Basic] -> where [Peek & Fire] you select [Enable].

*There are three [Lean mode] that you can see below [Peek & Fire] option. Below is the detail for [Lean mode].
Tap : If you tap on option, peek option will there until you tap again.
Hold : You will need to hold the button to peek and aim.
Mixed : It allows you to use both Tab and Hold option. You will need to tap to Peek. If you tap more that 0.3 seconds it will allow you to hold the button to peek and aim.

You can also click on (?) beside [Lean Mode] for instant information on this.

Furthermore, you can enable [Peek & Open Scope] option beside [Peek & Fire]. This option will allow you to peek while you using the Scope.

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