Thanks that you asked but before I will tell you that let me say something:
I would strongly recommend you to play the visual novel first because the OVA represents the game just a little bit and it is very complicated to understand if you dont have the VN experience plus you may get a distorted image of euphoria.
Now where to stream it: As far as I know there are currently no legal stream services available for an "offical" stream. There are services but they all are not that trustworthy. Just type euphoria ova in google search and you will find many sites.
But there is a legal way to official buy the OVA's: Its on DLsite.com . There you can buy all episodes of the OVA each costing 3,036 YEN aka 27.53 USD/23.49 EURO.
You can also buy the VN on there too but I would recommend if you want to play it in English to buy it on mangagamer.
I hope I could help you. By any other question feel free to ask me or join our community discord.