Find weakness in Tyler's gang guarding the church is a quest in Fallout 2.
This quest can be activated if you complete the quest Get permission from Metzger for gang war.
Go to the church where Tyler's gang is guarding the chemicals. Ask about what's going on: If you have a low CH, try using some alcohol on Tyler. Tyler will reveal that they are throwing a party. Unlike the previous speech check, this can be re-tried.
You cannot collect your reward from Lara: she will demand that you help her attack the gang.