$append

Update records by appending a specified value to the existing value in a column. The $append method is used to add new data to an existing value, typically for text columns, ensuring that the original value is preserved while the new data is appended.

await Member.$update({
    $where: { 
        age: { 
            $eq: 16 
        } 
    },
    $update: {
        $append: {
            username: 'sobes'
        }
    }
});