If you saved the config or the kernel source from the *old* kernel you can cat or less the .config in that directory, which is generally:
If you prefer the ncurses interface, you can:
And it *should* load the old kernel config.
You can also copy that old kernel config to new kernels:
cp /usr/src/linux-kernel-version/.config /usr/src/linux-new-kernel-version/
You run that command in the kernel source directory.
And that new config file is in the same place as the old one