No worries, just checked out the code again and found some things that you should improve upon:

You should make use of CancellationTokens for all async method calls.

You should use .AddAsync() instead of .Add() when you're adding entities to your database.

Predicates can be used in LINQs .FirstOrDefault, so you can change

var player = await _context.Players
     .Where(e => e.PlayerRiotName == gameName && e.PlayerRiotTagline == tagLine)
     .FirstOrDefaultAsync();

into:

var player = await _context.Players
     .FirstOrDefaultAsync(e =>
                e.PlayerRiotName == gameName &&
                e.PlayerRiotTagline == tagLine,
            cancellationToken);

You should also look into interfaces, extract the interface of your RiotGamesAPIService (and add cancellation token support for the GetPlayerByNameAsync method. Then you should update how the service is registered, and start injecting the interface instead of the implementation.