Change landing page permalink archive/landingpage_f/start

Hey, first of all: this works like a charm on my three wordpress sites that are linked via multi site plugin.
However, something is annoying.

The websites are
https://abenteuerwald-thale.de
https://brockensprint.de
https://ski-outdoorschule-schierke.de/

But when I put in the adress, it changes to https://abenteuerwald-thale.de/archive/landingpage_f/start

Everywhere it adds archive/landingpage_f/start
How can I remove that/change the permalink?

Thanks in advance