KYBO Website https://keepyourbootson.co.uk/
If you have not signed up to or joined England Rugby Referee Association would recommend that you do and that will also provide a number of development opportunities
There is also a facebook page for KYBO for those who use it which will also allow you to sign up and let you access all the videos and resources on there.
And unsurprisingly there is also a facebook page for England Rugby Referees Association
There are a plethora of video’s called Whistlestops covering a number of topics and are continually being added to.
If you have time on your hands, you might also like to look at the World Rugby site which has a training and development are where you can do a number of online modules. Link as follows: