C# update subarray by index in one query

Hello. i Have document with subarray:

     _id: 1,
    items: [
         { name: 'a' },
         { name: 'b' },
         { name: 'c' },

How i can update multiply items by index of subarray by C# in 1 query?

ps. I user strong-type C# + mongodb drivers.

$find: _id: 1,
$set: {items[1].name, “bbbb”}, {items[0].name, “aaaa”}

I try like this: but cant convert UpdateBuilder to UpdateDefinition

I try with combine: buy got error: “System.ArgumentException: Updates must have at least 1 update operator. (Parameter ‘update’)”