There is a knob in my garage which I have no idea what it goes it. I have turned it till it won’t turn both ways any nothing has happened that I could find.

Ohhh, THAT'S why my lights kept getting brighter and dimmer!

There is a chance it’s “outside” in some sort of deep box but that seems unlikely unless you are in the south.

You need a plumber unfortunately and if you really don’t have one it might be a grand or more. Schedule with water company to turn it off at the street, cut, add a good modern shutoff in a useful location (which might require changing layout) and so on.

Good luck, but I would not do it myself based on the comments so far. Just fyi.