Hello. I am here to help with the things Riot can't.
So the best thing is to take a rest from the game for a day or week. Not too long though, you will become weaker. Go and play a game that make you happy and helps you relax. The other best thing is to switch to normal (if you are playing ranked most of the time) and i reccomend blind. You can have a lot of fun there. You can take and try a new champion. This will help you relax with some new experience.
The most important thing is to just forget about this streak of bad games and enjoy yourself. After that return and keep learning new champs or practicing the old ones. This is the best thing you can do.
I hope this helped. If you have any other questions feel free to ask me. And best of luck in the fields of justice.