I think most courts today accept people not swearing, I think you can just "affirm" or even agree to tell the truth.
For the record, I am a Seventh-day Adventist although I was raised Catholic. But I don't think what I am is important. What is important is who Jesus is, and what He has done, is doing, and will do for us.
He is the eternal Son of the living God, Who took human flesh and became Emmanuel, "God with us." He lived a sinless life among us, then took our sins upon Himself and bore them in His body on the cross, where they separated Him from the Father and crushed the life from Him. As prophecy foretold, He was buried and rose again the third day, and ascended to heaven, where He lives to make intercession for us, to forgive us from our sins and cleanse us from all unrighteousness (1 John 1:9). He sent His Holy Spirit, the Third Person of the Godhead, to minister to us in His absence, giving us a new heart to enable us to keep His Word and live in obedience to Him, because we love Him (John 14:15). A day is coming when He will return to gather His elect, those who have accepted His sacrifice in their place by faith, and take them to be with Him in His Father's house (John 14:3) and "so shall we ever be with the Lord" (1 Thess. 4:17).