What needs explaining, trisher. I'm not sure I understand the question, but I'll have a go:
A transman is a woman who identifies as a man.
Women have cervixes, so transmen have cervices.
Cervixes can become cancerous, and smear tests can detect cervical cancer, so women are called for the tests.
Transmen, if they are being called for tests, must be on doctors' records as female, as that is what they are, so will be invited to attend for a test.
If they are not listed with a GP (perhaps because of moving house) their NHS number will identify them, but in any case they will be aware that their bodies are female whatever is going on in their heads.
Having made the decision to 'identify' as male, I assume that transmen will have considered their biology as much as, if not more than, the women who will also be invited for testing, so are at least, if not more likely to be aware of what a cervix is, and the fact that they have one.
So they are included in the invitations, and are at no more risk of cancer than other women. They are not being ignored, and they get the healthcare they need.
Have a missed anything?