How to windows application work online and offline c#

if create two setup files then Client need to two files download.....???

if you have already have online database then just give that database connection string into your winform app, then ship that to your client

for online you have to purchase a online mssql database and change connection string according to the credantial and when demo complete delete that database or make a function in your application that close automatically after some Duration. and for offline just install mssql database on client mechine and and change the connection string.