There are several ways to clear the SEL, one that can be performed locally and one remotely.
1. Clear the SEL locally
At boot, press ctrl-E to set the BMC ip address, in this same window you can choose to clear the system event log.
2. Clear the SEL remotely
If you have not already set an ip address for the BMC, do it now by pressing ctrl-E at boot. Besides configuring the ip address, enable IPMI too.
At the client be sure to have the bmc management utility installed, the default installation path is c:\program files\dell\sysmgt\bmc.
Perform the following command to clear the sel: ipmish.exe -ip 192.168.1.44 -u root -p calvin sel clear
To view how many entries are in the sel: ipmish.exe -ip 192.168.1.44 -u root -p calvin sel status