Relation Querying like a pro

I am a Parse beginner, I want to query from using [ParseQuery]
and I already have a relation object of User, and It already has user’s objects in.

And excludes all of that, I want to query avoid results of user’s relation object.
I am trying to write like this.

async function getItemsExcludeUserItems(request){

    var query = new Parse.Query('Items')
    var userRel = request.user.relation('usersItems')

    var userItems = await userRel.query().find({useMasterKey:true})
    for (var i of userItems){
    return await query.find({useMasterKey:true})

It seems inefficient way. How would you write in this case??

Best way in this case is to use doesNotMatchQuery: JavaScript Developers Guide | Parse