How do I change the UX here to signify rise or drop in percentage

I am trying to model a conversational chatbot and this is a relatively new area in terms of UX for me. I need to be able to set percentage increase or decrease alerts for my cryptocurrency bot something along the lines of "Alert me if BTC falls by 80% or ETH rises by 40%" I have the current UX designed as follows

What is the best way for me to get increase or decrease from the user? Currently if they mean -80, it translates to 80% fall in my bot but I dont feel this is optimal as the general user doesnt think in terms of negative numbers.