You give them the original, unencrypted source code. You can't edit ioncube encoded files.

Decoding an IONCUBE file is almost impossible as the coder encrypting the file picks a password of their choice which is used on the encryption algorithm that makes the final "Ioncubed" file. So you would have to know the password used by the coder, so your IT guy will have to email you the source code of the file to be edited so you can have those changes applied, then he can encrypt the updated files for you later when he comes back.