Hi Raphaëlle,
Welcome to Pix4D Community!
If you feel that some MTPs are incorrect, one way to proceed is by accessing the GCP / MTP Manager window by clicking Remove to delete a mark:
You could find more information about this workflow in the following support article: How to add / import GCPs in the Basic GCP/MTP Editor
You could also delete the entire point that is displayed on the GCP/MTP Table by also following these instructions: Menu Project > GCP / MTP Manager… > GCP / MTP Table > Remove Points
I hope this information was useful for you.
Dont hesitate to reach out if you need further assistance.
Have a very nice day.
Best regards,