I have a SIM card from Deutsche Telekom(https://www.telekom.de/hilfe/mobilfunk/mobiles-internet/mobilfunkstandards/apn-ratgeber?samChecked=true). From the above link and on my phone,one can read:
APN: internet.v6.telekom
I don't know if I will need a username and password after entering these data.
Probably, I should ask them as well.
Best wishes,