I believe you can find the contactinfo here

https://www.europarl.europa.eu/meps/en/home

5 july foundation wrote a blogpost about why we should send postcards instead:

Here is your chance to put pressure on MEPs to stick to their no to Chat Control 2 in a simple way.

As we have previously reported, there are signs that the European Parliament’s unanimous no to Chat Control 2 may be loosening - now that the EU elections are behind us.

So they may need some external pressure. This often happens with various email campaigns - which can easily be dismissed as spam and mass mailings.

However, something that usually bites is physical mail. Thousands of emails are the order of the day when things get heated in the European Parliament. But 25 physical letters are considered a public outcry.