Overall, the answer suggesting you get a professional to do it is the route to go. Make it someone else's problem and make sure to hold them accountable if they damage the counter.
Realistically though, if you get someone to show up at your home and pay them $30-75 like https://diy.stackexchange.com/a/211482/42053 suggests then accountability will be non-existent. At $30-75 you're just asking them to roll the dice because you don't have the equipment to do so. If this is a screwup then get the manufacturer to fix it because I sure as sin know that I wouldn't risk being held responsible for a couple grand countertop for $30-75 bucks. If they screw up then they'll just suggest a vanity cap and call it a day.
However, this forum post shares precisely your problem: https://www.ridgidforum.com/forum/mechanical-trades/professional-plumbing-discussion/42023-need-to-enlarge-a-granite-top-hole
Home depot now sells bits by ridgid that are an inexpensive diamond grit core bit.
The other way is to get a 1/8'' - 1/4'' carbide burr in a high speed dremel/ die grinder and route it out slowly.
I always use water/ wet sponge to keep the dust down and keep things cool.
I have the rotozip Floor Tile Bit XB-FTC1 1/4" diamond surfaced bit that I use in my rotozip for things like this and for some tile cutting and shaping. works awesome and is quite easy to control and handle.
I've never done this in granite so I can't tell you if it will work. It can be done in Corian.
Make a template in the diameter you want the hole to be in a piece of plywood. Make it big enough to provide a flat surface for your router to ride on.
Clamp or otherwise secure the template where you want the hole to be located, maybe some double stick tape will work.
Use your router and a carbide pattern bit to enlarge the hole following the pattern with the router and bit.
If you go with the RIDGID diamond bit in your drill, you can still use the template secured to the countertop with double stick tape.
Make the hole in the template the same size as the OD of the bit. Secure the template at the new hole location.
Now you can use the drill with less worry about the bit wandering.
I pick up the phone and call the nearest Granite fab shop. I don't do granite and I'm dang sure not paying to replace that high dollar slab when I mess it up.