You can contacr the school district and asked that he be evaluated. They will test him, even if he's been tested before. Once they complete the testing, they will prepare an IEP for your son.

Contact the Special Needs Preschool Department in the local school district in which you live. Tell them that you would like your 3yo with ASD to be evaluated to determine special education eligibility. Like previously mentioned by others, provide them with copies of any previous evaluations your son has had. If/when he's found eligible for sped services, an IEP will be developed with his IEP team which includes you as a vital/required member. Good luck! We are in the middle of the same process right now.

Call school superintendents office and ask to speak with the special education supervisor. You’ll need doctors notes listing your child’s diagnosis

go to the student support services and write that you want your child to have a IEP bring any testing you have and give them copys of everything