The registration service offered by RegisterToVote.eu, as reported earlier this week, which offered to submit details for people who filled in a form online, has been closed down by the Electoral Commission.
The Electoral Commission said: “We urge EU citizens that [sic] want to vote in the European parliamentary elections in the UK to only apply to register to vote through their local council or official websites. We welcome efforts by campaigners to encourage eligible electors to register to vote. However, our advice to anyone not yet registered is to only apply directly at www.gov.uk/registertovote.” (From: https://www.theguardian.com/politics/2019/may/04/site-claiming-to-help-eu-citizens-register-to-vote-is-shut-down)
Postal applications must be received by Tuesday 7th, which is difficult at the time of writing, as it's now Saturday May 4th, and Monday is a bank holiday. It is believed that very few of the over 3 million EU citizens in the UK who need to register to vote in the European Parliament elections have done so.
There is still a possibility that the elections scheduled for May 23rd might be cancelled but that becomes ever more unlikely as days go by.