"Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice: 32And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you." (Ephesians 4: 31-32)
Bitterness is not something that we have to "get rid of".
The original reading in the Greek shoud say "let it be removed.
We do not remove it, but the Holy Spirit ends up removing it as the same Spirit transforms us from glory to glory as we behold Jesus, our new and true self (2 Corinthians 3: 18)
Bitterness is not something that "you" get rid of, anyway, since this "bitterness", along with evil speaking and all the rest, merely pertains to the "old man Adam" which hangs on every human being, which has been crucified with Christ, and now we can enjoy His life.
God's betterness is greater than our bitterness. Let this Goodness, which we find in Christ, remove all bitterness from you as you grow in grace and knowledge of the Lord Jesus! (2 Peter 3: 18)