Just do it in steps.

Find a wide straight section and first try and ride with one hand. Slight but straight down grade does make it easier to start because there is less peddling effort.

Then when you feel confident, reach down and touch the bottle and keep peddling.

Then lift it out and put it back, while peddling.

Then reach down, take a drink and put the bottle back.

There are cages that make easier to pull the bottle out sideways.

And if you can’t get there you can mount a cage on the handlebars and use a camelback.

But even if you get good at it, everyone still has to plan a good spot to take a drink.

Years ago when everyone rode with diwntube shifters, riding with one hand was second nature.

John