Updating an object inside array using this.setState

Judging by how your data is structured, you may update it like this:

this.setState(prev => ({
  ...prev,
  userdata: [
    ...prev.userdata.filter(e => typeof e.isPro === 'undefined'), 
    { isPro: true }
  ]
}));

But if I were you, I probably going to make a function to update the state in the component class:

updateUserData(data) {
  this.setState(prev => {
    // make a copy of the previous state
    const copy = JSON.parse(JSON.stringify(prev));

    // assign values
    Object.entries(data).forEach(([k, v]) => {

      // find the entries that have the same key from the object that passed in
      const entries = copy.userdata.filter(entry => entry.hasOwnProperty(k));

      // If the entries exist, update them
      if(entries.length > 0) {
        entries.forEach(d => (d[k] = v));
      } 
      // otherwise, add a new entry
      else {
        copy.userdata.push({ [k]: v });
      }
    });

    return copy;
  });
}

And then update the data by calling:

this.updateUserData({ isPro: true, username: 'Bob' })

Then the state will be updated to

this.state = {
  userData: [{ id: 1 }, { username: 'Bob' }, { isPro: true }]
}

You can make a copy of the array, then find the index where the dictionary you want to modify is, and then modify it:

UPDATE (sorry about misprints, fast writing...)

    let userdatadummy = [...this.state.userData]
    const k = userdatadummy.findIndex((item)=>Object.keys(item).includes('isPro'))
    userdatadummy[k]['isPro']=true
    this.setState({
        userData: userdatadummy
    })