Hello and welcome to the forums.
I’m going to ignore the fact that checking for a specific actor using its hardcoded name is probably not the best idea.
With your current setup this would be how to change the text:
First you have to cast the AActor you’re getting from your TActorIterator to ATextRenderActor.
Then you’d check whether the cast succeeded or not by comparing the result of the cast to NULL/nullptr.
If that worked you can use the pointer to call GetTextRender() which returns a UTextRenderComponent*.
Again check whether this pointer is not NULL/nullptr.
If this was successful again you can finally use the UTextRenderComponent to access and change the Text UPROPERTY. But do not change the property manually, use the SetText function instead!
ATextRenderActor* TextRenderActor = Cast<ATextRenderActor>(*ActorItr);
UTextRenderComponent* TextRenderComponent = TextRenderActor->GetTextRender();
TextRenderComponent->SetText(/*YOUR TEXT AS FText HERE*/);
//failure handling (TextRenderActor didn't have a valid/non-NULL TextRenderComponent)
//failure handling (cast failed)
If you’d use TActorIterator<ATextRenderActor> instead, you’d no longer need to cast and can work directly with the iterator.
NOTE: the above code hasn’t been compiled or tested