Vigilance.
As soon as the pup looks like it MIGHT want to go, silently and with no show of emotion, pick them up (even if they have already started, or even just finished) and place them outside. Once down, behave normally.
If they haven't started to go within a minute or two, let them follow you inside.
As soon as they start to go, gently use your pre-chosen 'toilet word' something you don't mind saying in public. We use 'Whizz', but you can use any word.
Repeat it over, gently, until pup is done, at which point, there needs to be lots of over the top 'GOOD BOY!' and smiley faces. All this needs to come the very second pup finishes. A small treat is a great idea. Then let them follow you inside.
If you miss an 'accident' indoors, don't punish the pup, they don't realise the association after more than a minute, or even less. PLEASE don't rub their nose in it, they don't understand.
Our current pooch (Working cocker) was trained, fully, in 2 days. By day 2, he'd take himself outside for his toilet, and pee on command ('Whizz') by day 5.
They'll want to pee a few times an hour at this age, so you'll get lots of practice, ESPECIALLY after they've had a nap. Don't be afraid to wake them up from a nap to practice this either. Wake up>notice you>need to pee.
Hope that helps, and yes, I do work with animals.
Steve