Since we believe that the OT saints were saved the same as NT saints with their souls going to heaven upon death and retrieving their new bodies at the Second Coming.How did Moses have his glorified body at the Transfiguration?

1. Jesus was transfigured, but the text doesn't say that Moses nor Elijah had transfigured bodies.
2. The general truth is that the "incorruptible body" (cf. 1Cor 15:51-54; 2Cor 5:2-4) of which Paul, by the inspiration of the Spirit writes about will be given at Christ's second (final) coming which will usher in the Great White Throne Judgment. However, is it beyond God's ability to create the spiritual bodies intended for Moses and Elijah at any time He desires? Remember that what was seen on that mountain was a vision (Jh 17:9). In this special case, the vision happened to display the deity of Jesus the Christ and the fulfillment of OT prophecy with examples of two of the 'types' which foreshadowed His coming. In another event, God used the resurrection of Lazarus to demonstrate the identity and deity of the incarnate Son of God and secondarily to dramatically demonstrate the reality of the resurrection.

So, I do not believe the passage you are most likely referring to in Matthew actually states that Moses and Elijah had "glorified" bodies, i.e., the permanent future bodies which all the saints of God will receive and occupy on the New Earth.