Would like to check where should i change the file for RHEL 8? I found the below link but doesn't work for rhel 8. 

Common issues :: NXLog Documentation

This scenario requires edits to the service file or an override. To check NXLog system limits, use the following command:

$ cat /proc/$(cat /opt/nxlog/var/run/nxlog/nxlog.pid)/limits

On Systems not using /proc, check the system’s open file limit:

$ sysctl kern.maxfiles

To adjust limits for nxlog, create /etc/systemd/system/nxlog.service.d/override.conf and add the following definition:

[Service]
LimitNOFILE=100000

Update the service settings with:

$ systemctl daemon-reload