How to connect with the Google ad manager(**GAM*) for *prebid video ads**

How to connect with the Google ad manager(GAM) for prebid video ads where I created the video ad units and line items and creatives in my google ad manager account and I also created the vast url tag. I am not getting how to add the vast tag or video unit in my website using prebid.js.I am new to prebid.js

I have the following example from prebid examples

<script>

    var pbjs = pbjs || {};
    pbjs.que = pbjs.que || [];

    var googletag = googletag || {};
    googletag.cmd = googletag.cmd || [];

    var PREBID_TIMEOUT = 1000;

    var adUnits = [{
        code: 'video1',
        mediaTypes: {
            video: {
                context: 'outstream',
                playerSize: [640, 480],
                mimes: ['video/mp4'],
                protocols: [1, 2, 3, 4, 5, 6, 7, 8],
                playbackmethod: [2],
                skip: 1
            }
        },
        bids: [
            {
                bidder: 'appnexus',
                params: {
                    placementId: 13232385
                }
            }
        ]
    }];

    pbjs.que.push(function () {
        pbjs.addAdUnits(adUnits);
        pbjs.requestBids({
            bidsBackHandler: initAdserver
        });
    });

    function initAdserver() {
        if (pbjs.initAdserverSet) return;
        pbjs.initAdserverSet = true;
        googletag.cmd.push(function () {
            pbjs.que.push(function () {
                pbjs.setTargetingForGPTAsync();
                googletag.pubads().refresh();
            });
        });
    }

    setTimeout(function () {
        initAdserver();
    }, PREBID_TIMEOUT);

    googletag.cmd.push(function () {
        var slot1 = googletag.defineSlot('/19968336/prebid_outstream_adunit_1', [[1, 1]], 'video1').addService(googletag.pubads());
        googletag.pubads().disableInitialLoad();
        googletag.pubads().enableSingleRequest();
        googletag.enableServices();
    });

</script>

Prebid Outstream Video Ad

googletag.cmd.push(function () { googletag.display('video1'); });
    </script>
</div>

what changes I can do the above code so after making changes I will get the ads in my website using my own AdUnit or lineitem which I have cretaed in my GAM.
If DSP is required to test, Is there any possible thing I can add my own video or video url in the Google Ad Manager
Or What I can do with my vast url tag where to add vast tag or implement that I am really confused what to do can some one help??