Hopefully this will help. According to this manual, holding down the "X" button will disconnect.
https://www.yaesu.com/downloadFile.cfm?FileID=15214&FileCatID=263&FileName=FT3DR%5FDE%5FWIRES%2DX%5FENG%5F1908%2DB.pdf&FileContentType=application%2Fpdf
Not sure this works..??
With my FT-3DE
> Press the X to get the radio into Wires X mode
> I connected to "Parrot", to test it works OK, and it did.
> Press and hold X, the Radio drops out of X mode
> Key Radio and Talk... It is still connected to Parrot