Let's say party A has won 3 seats out of 10 seats in South East Region of UK in the recent European Parliament election.
How does that party choose 3 out of its initial 10 MEP candidates whose name are shown on the voting ballot paper?
The EU party lists are ranked. So when the party earned 3 seats, the top 3 people on their list become MEPs.
The list ranking order is determined by the party through an internal process.