No option for the the capacitor diameter I require


i am designing a PCB that has a 6x11mm Electrolytic Capacitor capacitor.
i can find 100,200 and 300 mil capacitors in Fritzing.

how can i adjust the diameter or find other options?

It isn’t clear to me (and I expect others) what you are asking for. Is the pin spacing something other than 100 to 300 mils or are you wanting a larger case outline? Probably for any non standard layout you would need to create a custom part (or get one of us to do it for you). A good start would be the data sheet for the capacitor in question with foot print and case size preferably.