Need help finding an Aux 3.5 to fm transmitter that fits in a car plug

I need help finding a Aux 3.5 to Fm transmitter that fits in a car plug, I’m trying to get the audio from my external car play device into my cars speaker but my ace doesn’t come with an aux plug so I need some help finding a device that will bring audio from an aux cord to an fm radio so that I can use my cars radio to play the audio. I’m looking for a device that can specifically pass the audio not an aux or fm transmitter Bluetooth device. Any suggestions would be immensely helpful, thank you.