Find the kernel version you need in http://mirror.centos.org/centos/7/rt/x86_64/Packages/
Take kernel-rt-3.10.0-693.2.2.rt56.623.el7.x86_64 as an example
After downloading, execute
yum install kernel-rt-3.10.0-693.2.2.rt56.623.el7.x86_64.rpm
Or execute
rpm -ivh kernel-rt-devel-3.10.0-693.2.2.rt56.623.el7.x86_64.rpm
If you are prompted that the relevant package is missing, install the relevant components according to the prompts, usually the relevant components can be found on the http://mirror.centos.org/centos/7/rt/x86_64/Packages/ website
After the installation is complete, restart the computer and select the kernel you want to use in grub.
carried out
uname -rms
Check whether it is the installed kernel.
Complete the kernel installation