pre-fill form and then let toUpdate

function saveProperties() {
    $w('#buttonSubmit').disable();
    let user = wixUsers.currentUser;    //<---here you get the USER GOOD!
    let userId = user.id;               //<---here you get the USER-ID GOOD!
    let myQuery = wixData.query("Properties") //<--- here you get all data from your PROPERTIES-DB, GOOD!
    myQuery.eq("_owner", userId).find()
    .then((res)=>{console.log("RESULTS: ", res);
        //not so good!
        /*
        let toUpdate = {
            let toUpdate = {
            "industry2": $w("#checkboxGroup1").value,
            "title": $w("#input2").value,
            "agentEmail": $w("#input3").value,
            "mapLocation": $w("#input36").value,
            "businessWebsite": $w("#input35").value,
            "facebook": $w("#input33").value,
            "instagramLink": $w("#input34").value,
            "hoursOfOperation": $w("#input37").value,
            "description": $w("#richTextBox1").value,
            "familyPic1": familyPhoto1,
            "familyPic2": familyPhoto2,
            "amenities": $w("#selectionTags1").value,
            "_userId": userId
        };
        */

        // using instead....(direct way)
        let items = res.items; console.log("ITEMS: ", items);
        if(items.length>0){console.log("Length > 0 !");
            let firstItem = items[0];
            firstItem.title =           $w("#input2").value;
            firstItem.agentEmail =      $w("#input3").value;
            firstItem._userId =         userId
            firstItem.industry2 =       $w("#checkboxGroup1").value;
            firstItem.mapLocation =     $w("#input36").value;
            firstItem.businessWebsite = $w("#input35").value
            firstItem.facebook =        $w("#input33").value
            firstItem.instagramLink =   $w("#input34").value
            firstItem.hoursOfOperation= $w("#input37").value;
            firstItem.description =     $w("#richTextBox1").value
            firstItem.familyPic1 =      familyPhoto1;   // where does this come from ?
            firstItem.familyPic2 =      familyPhoto2;   // where does this come from ?
            firstItem.amenities =       $w("#selectionTags1").value;
            //--------------------------------------------------------------------------
            wixData.update("Properties", firstItem) 
        }
    });

Where do these values come from ?

 firstItem.familyPic1 = familyPhoto1;   // where does this come from ?
 firstItem.familyPic2 = familyPhoto2;   // where does this come from ?

Where do you declare → familyPhoto1 / familyPhoto2 ???

How do I get the file upload fields to prefill with what is already in the database?
Which are your → file upload fields
How does it look like inside your database?

Just you know the structure of your own database.