Its a simple general approach, in Setup search for nagios and you will find the rule. In the rule enable inline help (Help → Enable inline help)
The plugins are in the mentioned default folder:
OMD[XXX]:~/lib/nagios/plugins$ ./check_http -H xxx.yyy.corp -C 14 -t 1
OK - Certificate 'xxx.dd.ff.cc' will expire on Thu Jun 26 13:49:59 2025 +0000.