What is the iOS equivalent of the android three dot menu icon?

It's : ellipsis

and you can use it like this :

Image(systemName: "ellipsis")

I myself use the "square.and.arrow.up" system icon as my equivalent. Though the Android icon isn't so terrible you could implement it yourself.

Additionally a bottom action sheet is a great equivalent for Android's Contextual Menu.

SwiftUI Implementation of action sheet

.actionSheet(isPresented: $showingActionSheet) {
    ActionSheet(title: Text("Change background"), message: Text("Select a new color"), buttons: [
        .default(Text("Red")) { self.backgroundColor = .red },
        .default(Text("Green")) { self.backgroundColor = .green },
        .default(Text("Blue")) { self.backgroundColor = .blue },
        .cancel()
    ])
}

In iOS 14 Apple introduced Pull-Down menus. It should be the closest thing to Android overflow menus. For example, you can add a "more" bar button item to your navigation bar and attach a menu to it.

You can find details about it here: https://developer.apple.com/design/human-interface-guidelines/ios/controls/pull-down-menus/