Below you can find a selection of websites where your child can use dienes in an online format to assist with their learning.
I would recommend the top marks site as there is a button where they can check if they have made the correct number. However, if using this site please point out to your child that the 'u' column means units and this is the same as ones.
Alternatively below the websites is a worksheet where they can cut out the dienes and physically make the number. Some children may prefer this and if you write the required numbers down gives them time away from the screen.
There is exactly the right number of dienes on this worksheet which will tell you if your child has got the correct amount overall.