Hearing on Custody Modification?

Father is currently under investigation with the police department based on allegations of abuse of our child.  There is a joint custody agreement in place and a final judgment was entered on the divorce days ago.  I filed an OSC ex parte to change the custody agreement pending the outcome of the case and the judge flat out denied it based on hearsay problems.  He set the next hearing to hear the modification.  What do I need to do at the next hearing? Do I bring witnesses? Evidence? Is it a mini-trial? – Kortney