This dissertation presents a search for the electroweak pair-production of charginos and the associated production of charginos and neutralinos in the B−L Minimal Supersymmetric Standard Model with spontaneous R-parity violation. The chargino and neutralino each decay via R-parity violating couplings to a charged lepton or neutrino and a W, Z, or Higgs boson. This analysis searches for resonances in the trilepton invariant mass spectrum, targeting events with charginos decaying to three electrons or muons via a leptonically decaying Z boson. The dataset includes 139 1/fb of 13 TeV proton-proton collisions produced at the Large Hadron Collider and collected by the ATLAS detector. With no significant excess observed, limits are set on chargino and neutralino masses between 100 GeV and 1100 GeV, depending on the assumed branching fractions to leptons (electron, muon, or tau) and bosons (W, Z, or Higgs).