3rd-party certificates in FR3

Hello everyone! I'm using freeradius 3.0.9. And i want to realize next scheme: cisco wlc wi-fi -> freeradius -> mysql db. It's all ok with db, i just want to clear out the messages to end user about radius certificate. So, i want use a certificate, which root ca will be in apple\android's certificate stores. Maybe geotrust, maybe other. I didn't find how it should to install and i need help here. Thank you. tl;dr I need a cookbook how to setup chained certificate from other trusted root CA. -- BW, Ivan.