ReactJs- Re-call self-invoked function "function ()"

I recently started an App in ReactJs and there are some areas where I still lack some knowledge, so my question may be a bit basic. Analyzing the following code:

updateContent(mainUrl){
        console.log("updateContent was called")
        fetch(mainUrl)
            .then((responseJsonAnyUrl) => responseJsonAnyUrl.json())
            .then((responseJsonAnyUrl) => {
                this.setState({
                    mainUrl: mainUrl,
                    jsonObject: responseJsonAnyUrl
                },
                function testName() {
                    let interval = 20000
                    let ind = this.child.current.getCurrentIndex()
                    let zlengths = this.child.current.getZoneLengths()
                    let option = 1
                    if (ind !== zlengths[0]-1){
                        //didn't iterate trough all content, can't update
                        option=2
                        interval = 5000
                    }   
                    console.log('ind', ind)
                    console.log('len', zlengths[0]-1)
                    console.log('interval', interval)
                    this.timeout = setTimeout(
                        function(){
                            if (option===1){
                                this.updateContent(mainUrl)
                            }else if (option===2){
                            //  call testName()
                            }
                        }.bind(this, mainUrl)
                        ,
                        interval)
                }.bind(this))
            })
    }

I have a " self-invoked function() " which I gave the temporary name: " testName ".

In the 2nd comment, I want to be able to call testName() again, but I could not find the right syntax to do it. How can I call it correctly?

Note: I leave the link for the class / component where this method is found, in the case of be useful.