This is not an instant fix, by the way; it takes time and practice.
2. Ssssssslllllllllllooooooooowwwwwwwlllllllllllyyyyyyy practice the passage until you at the very least get the sound you want.3. Bring it up to tempo, but always keep that sound in your mind and make sure you are producing it even at faster tempos.
Outin you're advancing if you know the problem exists ! It's that simple and now you can work to solve the problem ( and obviously you are doing just that). In the beginning we know nothing, we take baby steps and eventually learn to play well. It's a long term investment.