I moved your post here to avoid duplicate topics … already mentioned here were this support article …
https://support.fairphone.com/hc/en-us/articles/210512123
… as well as this …
… and in English it’s called factory reset, which can be found in the Settings.
Please keep in mind that this is a community forum, not the company.
If you want to contact the company, contactsupport has all the info.