Don't think you can really, not if not reaaly verbal. Sorry.
We have ds (22 months) and dd (1 week). Ds has started saying "noooo" to everything, just in the last week-never did this before. Largely ignores her but asks us to put her down if we hold her. Wants her to go back now.
He also seems very angry with me, and anyone else who holds the baby.
I think just hang in there. I hated my brother when he was born + now, despite being completely different we are close. dp + his brother apparently bonded immediatrely (MIL says, as another helpful example of How We Have Failed As Parents-but dp does agree)-and hardly speak now-not even a card/phone call after dd's birth!
Get lots of videos in + make sure house is fairly childproof, if you intend to bf. Its a few weeks before you can bf while running after a toddler.
Make + freeze him food he likes and get him some new toys to play with, ones that don't require you so much. If you possibly can, get him used to playing independently.
Get help with him for the first few weeks, if humanly possible.
Good luck. Sorry this isn't more positive-its only been a week and I think maybe dp and I are strugglung a lot because we are both elset children.