How would I go about removing the splash damage that lowers the users health?
I want to make it normal splash damage

SetPlayerIgnoreRadiusDamage( true );

having this on will ignore all RadiusDamage
other than using this you would have to do a damage override script
to ignore any self damage from the Wunderwaffe or add somthing in

player_damage_override( eInflictor, eAttacker, iDamage, iDFlags, sMeansOfDeath, sWeapon, vPoint, vDir, sHitLoc, modelIndex, psOffsetTime )

in _zombiemode.gsc to not affect you from the Wunderwaffe and if it ShellShocks you use this

self StopShellShock();

in player_damage_override have it check if the damage is coming from the wonderwaffle and stop it there

no there is a "actual" fix, was posted like 8 years ago, use the search bar

the problem is the wonderwaffe specific code keeps /2 the players "max" health instead of health, so eventually your max health becomes "1"