Calling functions from other c++ classes

I have a class called ATimer. It has a timer and when the timer ends it calls its own function CountdownHasFinished(). That function has to call a function from the class APlayer. That function is called StartMoving(). How do I do that in c++ or is there another way to do basically the same?

ATimer.h (simplified)

#pragma once

#include "GameFramework/Actor.h"
#include "Timer.generated.h"

UCLASS()
class QUICKSTART_API ATimer: public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ATimer();

	// Called when the game starts or when spawned
	virtual void BeginPlay() override;
	
	// Called every frame
	virtual void Tick( float DeltaSeconds ) override;

	void CountdownHasFinished();

FTimerHandle CountdownTimerHandle;
};

APlayer.h (simplified)

#pragma once

#include "GameFramework/Pawn.h"
#include "Player.generated.h"

UCLASS()
class QUICKSTART_API APlayer: public APawn
{
	GENERATED_BODY()

public:
	// Sets default values for this pawn's properties
	APlayer();

	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

	// Called every frame
	virtual void Tick(float DeltaSeconds) override;

 	void StartMoving();
	
};

Well your Timer needs to find a reference to your APlayer in some way. Could you provide more details about who owns the timer and what it has access to? Some approaches would be:

  1. Have the Player register itself with the Timer in some way (either directly or via some delegate pattern, although I’m not sure which of those are supported by the Unreal framework).
  2. In Timer CountdownHasFinished() you could use an actor iterator to find all instances of APlayer
  3. Make the Player the owner of the Timer so it knows about it explicitly

In short, there are many options that can be good or bad depending on your setup.

Updated the question. Does it provide enough information now? The 3rd option seems to be the right approach for my situation. Could you please provide some example code/ a link to a website?