re: "My client is offline after delivery."
Clients are not be required to be online.
In fact, I advise you to not know one way or another if your client is "online." Don't look at the stalker dots. I never do.
re: "I had submitted and requested payment after job is done."
Good. That is what you are supposed to do.
re: "After that he is offline for 3 days."
As is his right. You don't need him to be online. You don't need him to do anything.
re: "What should i do?"
You should do nothing.
If the client does NOTHING then Upwork will release ALL of the escrow money to you AUTOMATICALLY.
I can see in your screenshot that you already clicked the "Submit Work and Request Payment" button. You did that 3 days ago. The client will manually release the money to you when he is ready to do so. If he DOES NOTHING then you will automatically see the money go to you in 11 days.
DO NOT click the Submit button again. That resets the time and makes you wait LONGER.
Do not send additional messages to the client.