Activate Phyrexian Altar six times by sacrificing Gerrard and five other creatures, adding ({5} magic symbol) ({B} magic symbol) .
Gerrard dies, triggering its ability.
Holding priority, activate Kenrith's last ability by paying ({4} magic symbol) ({B} magic symbol) , returning Gerrard from your graveyard to the battlefield.
Resolve the Gerrard trigger, returning all artifact and creature cards put into your graveyard this turn to the battlefield.
Repeat.
Once you have infinite colored mana, you may use it to activate Kenrith's other abilities.