1. Access OpenVZ 7 node via SSH and install required template with the command:

yum install centos-7-x86_64-ez

The template name always has the structure {distribution}-{release}-{arch}-ez. As an example centos-7-x86_64-ez

2. Access the master node via SSH and create a file under /vz/template/cache directory.
The file name should be a template name with tar.gz extension. In our example the name would be centos-7-x86_64-ez.tar.gz:

touch /vz/template/cache/centos-7-x86_64-ez.tar.gz

After that just follow the usual instruction for registering templates.