How to rotate Character BP`s Spring arm with using bUsePawnControlRotation as true?

Development Programming & Scripting
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1

Hello. This is my first step with Unreal Community.
I have some problem with my project.

// Setting for SpringArm
CameraBoom = CreateDefaultSubobject<USpringArmComponent>(TEXT("CameraBoom"));
CameraBoom->SetupAttachment(RootComponent);
CameraBoom->TargetArmLength = 500.0f;
CameraBoom->bUsePawnControlRotation = false;
CameraBoom->SetRelativeRotation(FRotator(0.0f, -20.0f, 0.0f));

Above code is my first try.
But after playing, I recognized cameras rotation following characters rotation.
In view of player, It makes me hard to concentrate to game.

So I changed my code like this.

// Setting for SpringArm
CameraBoom = CreateDefaultSubobject<USpringArmComponent>(TEXT("CameraBoom"));
CameraBoom->SetupAttachment(RootComponent);
CameraBoom->TargetArmLength = 500.0f;
CameraBoom->bUsePawnControlRotation = true;
CameraBoom->SetRelativeRotation(FRotator(0.0f, -20.0f, 0.0f));

However, above code made another problem.
In my character blueprint, spring arm`s rotation can not modified anymore.

So my main question is
How to rotate Character BP`s Spring arm with using bUsePawnControlRotation as true?

If you know some solution. Please share with me.
It will be very helpful for me.

Thank you for your time to read this.