As an advanced learner, building an accent is a matter of doing three things:
1. Ear training
2. Pronunciation practice
3. Habit creation
Our pronunciation trainers are really good at addressing the ear training portion, even for advanced learners. You may want to skip some of the more obvious flashcards (in Anki, hit the exclamation point to suspend cards that feel too easy), but definitely take advantage of the minimal pair training to help build your ears.
For pronunciation practice, use the videos that come with our trainers. Watch them once before you use the trainers, just to get oriented, but then make sure to watch them after as well - once you can hear all the sounds in a new way, you should be able to use the information in the videos to better pronounce those sounds.
Last is Habit Creation, and it's the hardest part. As an advanced learner, you've been practicing with a non-native accent for a long time. This means you have deeply ingrained speaking habits that are non-native, and those habits will never completely disappear. But (!!) you can create NEW habits next door. Practically, this means that you're going to train like an actor. You make a 'character' in your target language that pronounces everything perfectly (as you learned from the pronunciation trainer). It will not feel like your own voice. Then you practice speaking as if you were this new, native-accented character. It will feel like you're playing a silly game at first, and the more time you give it, the easier it will become. Over time, your goal is to become more familiar with 'acting' in your target language than you are 'speaking' it with your original accent. At that point, you reach your goal. You'll still be able to flip back to your original accent (as I said, that habit won't disappear), but you'll be able to choose to speak in the 'actor' accent easily, and that's the accent you want to actively choose each time you speak.
I hope that clarifies things a bit!