Step 1: Open Microsoft Bot Framework Composer
Step 2: Select the bot bot12345678
Step 3: Open the Configure page in Composer. Then select the Development resources, and scroll down to Azure QnA Maker.
Step 4: To access the Connect to QnA Knowledgebase action, you need to select + under the node you want to add the QnA knowledge base and then select Connect to QnAKnowledgeBase from the Access external resources action menu.

Step 5: Review the QnA Maker settings panel after selecting the QnA Maker dialog.
Use:
Instance: bot%@lab.LabInstance.Id-qna-qna%
Reference:
https://docs.microsoft.com/en-us/composer/how-to-create-qna-kb
https://docs.microsoft.com/en-us/composer/how-to-add-qna-to-bot