Oh dear.. im not sure if yours can still be used. But, normally, I use cooking artificial vinegar and pour it in my steriliser. I leave it in for 30 mins then scrub.
I never bother to sterilize any items while my gals were babies. Now, they are all super healthy and strong and they seldom fall sick. 😊
looks like it really needs a good wash. Personally I don't use steriliser as I don't c the need to