dnf

https://ask.fedoraproject.org/en/question/51444/how-to-install-specific-kernel-version/

You can use yum and list all kernel versions that are available (from the enabled repositories at your system) with the following command

yum list --showduplicates kernel

If the kernel you want is on the list, you can install it directly with yum.

yum install kernel-<and the version here>

If you want another kernel that is not listed, you can search at Koji download and install with rpm --oldpackage (as indicated at the link you've provided

or you can even try yum.

You have to know that,

It is stronly recommended, always using the latest stable kernel version that Fedora provides.

Last, but not least, you should exclude the kernel updates from yum, through the /etc/yum.conf file.

Append

exclude=kernel

at the end of the file. This should do the trick. That way, yum will not update the kernel(eg 3.14 version) with the latest (eg 3.15) version.