This is done in the voice grouped-trunk section of the configuration. Assign each PRI a different trunk number. Create a voice grouped-trunk referencing each trunk and list the matching DIDs that you want routed to that PRI under it. You can also assign a cost metric to each so that if one PRI is busy or down the other will be used as a backup.
You can also route calls based on the originating number rather than the destination using SABR (Source ANI-Based Routing). Details here: https://supportforums.adtran.com/docs/DOC-1862