PIP 2nd appointment

How very odd. I've never come across this before.
I can only assume that Atos (IAS) / Capita etc have made a complete organisational horlicks of your first assessment, and have not managed to forward a copy to the DWP decision-maker.

I'm afraid you will have to go along to this next assessment, and treat it as your first.
(At least you will know what form it takes).

Take a copy of your PIP form with you.
Some useful info on assessments:
https://www.citizensadvice.org.uk/benefits/sick-or-disabled-people-and-carers/pip/help-with-your-claim/your-assessment/
https://www.benefitsandwork.co.uk/personal-independence-payment-pip/pip-medical-assessments

If you can, take someone with you. Ask them to make notes through the assessment re Q's & A's.

When the dust has settled you may think about making a Subject Access Request to the assessment company to get your records and see what the failure to complete your first assessment was.
And, perhaps, to the DWP:
https://www.gov.uk/guidance/request-your-personal-information-from-the-department-for-work-and-pensions

Try not too stress about it too much.
Do some preparation instead.
Go through the descriptors, identify those which get you the necessary 8/12 points, and have some examples written down (or a diary of a typical week/month) to take with you and tell the assessor about.
Remember reliability, and if it takes you twice as long to do an activity then you should be assessed as not being able to do it - with COPD this might be the case for a quite a few activities (dressing / washing / etc).
The PIP assessment guide is helpful on reliability.
Also remember the "majority of time" rule - i.e if you can't reliably do an activity for 50% of the time over a year - then you should score points.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/725533/pip-assessment-guide-part-2-assessment-criteria.pdf

From Benefits & Work -
"It's vital that, before you complete your form, you understand that just because you can carry out an activity, that does not mean you are prevented from scoring points for being unable to do it.
Guidance issued by the DWP states that you need to be able to complete an activity
- reliably in order for it to apply. According to the guidance, reliably; means whether you can do so:
- Safely; in a fashion that is unlikely to cause harm to themselves or to another person.
- To a necessary and acceptable standard given the nature of the activity.
- Repeatedly; as often as is reasonably required.
- In a reasonable time period no more than twice as long as a person without a physical or mental health condition would take to carry out the activity."

Good luck.