What’s the best way to train my puppy to ring a bell to potty?

I'm trying to train my puppy (4 months old) to ring a bell to go downstairs to potty. I use a small patch of grass, but he'll go even on a pee pad if its in the same spot. Ideally, I want him to think ring bell -> alert human -> go downstairs -> go potty.

The reason that I want him to learn bell = potty is so that I can clean his paws and poop after he goes downstairs and eventually, I'd like to bring him outside anytime he needs to potty and I want him to be able to let me know that he has to go.

I've pretty much gotten him to go to potty downstairs 100% of the time now (finally). He will always make his way downstairs to go potty. However, the problem is that he isn't spot on with the bell ring. I think he just associates the bell with "downstairs." Sometimes he will ring it to go potty but sometimes he rings just to explore downstairs. He occasionally likes to go downstairs to explore. It's not a big area but it is where my front door and shoes are so I imagine there is lots of smells that he wants to sniff. Sometimes he doesn't ring at all and just goes downstairs. Sometimes he stands at the top of the stairs staring at me until I go ring the bell for him and he will go downstairs when I do. Lots of variance lol

What is the best way to train him to 100% of the time ring bell -> downstairs -> potty? I thought maybe training him by making him ring bell, going downstairs & treating a bunch of times but then I fear he'll just learn bell is downstairs.

Any advice appreciated, thank you!

TDLR: I want my puppy to ring a bell to go downstairs to go potty. I want him to only ring the bell when he needs to go potty and never to just play or explore downstairs / outside.