Beh button to change data source

New to Bokeh, making a visualisation application with two data sources.
I want to make a button which will help me change data sources. I tried my best to understand, Button is getting created but it is not working. Can someone help me writing a simple prototype ?

df = First.csv

Function: (… ABC source = df …)


(… change as df = Second.csv…)

call Function


such type of simple program is to be made.