Attention is less something you summon than something you stop leaking. Nobody has ever concentrated harder by trying. They have closed the eleven small doors it was escaping through.
The phone in another room rather than face-down on the desk. The tab closed instead of minimised. A note made of the thought that arrived mid-task, so it stops circling back to check you received it.
What is left afterwards is not superhuman. It is your ordinary attention, finally uninterrupted, which is already more than most people get in a week.