Get character to use custom character movement component

You can override Character Movement Component in the constructor.
Instead of use default empty constructor, replace:

AMyCharacter::AMyCharacter()

to

AMyCharacter::AMyCharacter(const FObjectInitializer& ObjectInitializer) : Super(ObjectInitializer.SetDefaultSubobjectClass<UMyMovementComponent>(ACharacter::CharacterMovementComponentName))

Although it is for an older engine version, the Rama wiki it’s a usefull resource:

https://wiki.unrealengine.com/Custom_Character_Movement_Component