Formatting Agent Block Responses

I have a function that splits a paragraph into shorter sentences. When I used prompt blocks, I could easily use this function because I was able to store the prompt's response in a variable. However, I’m having trouble doing the same with an Agent block response.
How can I store the Agent block's response in a variable or make the Agent reply in shorter, separated sentences instead of one long paragraph?
I’ll be using this on WhatsApp, so shorter messages are better than large blocks of text.