I've lost my superadmin certificate/My superadmin certificate has expired

You have brought shame upon your dojo. Never fear though, you can solve this from the CLI:

$ bin/ejbca.sh ra setuserstatus superadmin 10 
$ bin/ejbca.sh ra setclearpwd superadmin password 
$ bin/ejbca.sh batch 

You can now remove the old P12 if still available and import the new one to your browser.