I get that you are using a default knowledge base, in order to use your customs qanda pairs you can upload the knowledge base in the source field for example you can create an xl sheet with 2 columns one for questions and one for an answer, this is a simple knowledge base you can insert it in the source field then deploy the knowledge base and then you can test and the custom responses will be generated from your knowledge base.
Find the screenshot above and select source and insert you KB.
If this helps kindly accept the answer thanks much