I need the anti theft code for the radio

If you changed the battery and the theft lock engaged you can try the onboard reset. Press and hold the radio power button for at least 2 seconds, this will usually reset the unit so it turns on.
If however that doesn't work and you cannot find the code written in the owners manual or on a sticker stuck inside the glove box on a sticker like the image shows (the RH number would be the serial number and the sticker with two numbers is the serial number and code, if you find that sticker you turn the key on, turn the radio power on and enter the code using the radio preset buttons) you will need to do one of two things, the easiest is to visit a dealer, you will need the registration for the car and ID showing you own it. They will then call in and get the correct code.
The other method takes longer but you don't need the dealer. However you do need a few things:
Your zip code
Your phone number
A valid Email
The cars VIN number
The Serial number for the radio, this will be on a tag on the radio itself and the radio will have to be removed to read it, unless the tag with the serial number is on the glove box.
Now you visit this site and enter the information as it is requested and they will send you the code. https://radio-navicode.honda.com/
If this radio came from a different vehicle then you will need that vehicles VIN number instead of the vehicle it is installed in.

To remove the radio you need to remove the center panel it mounts in and then get the serial number off the chassis of the radio.