A family of Microsoft word processing software products for creating web, email, and print documents.
Hi Marcin Siemion,
If you want to change Trusted locations in Office 365 apps, please try steps mentioned in the article below. Open other Office apps for configure this setting.
Add, remove, or change a trusted location
At the bottom of the trusted locations dialog there is a check box that says Allow Trusted Locations on my Network (not recommended). You will have to check that box to use a network location. With that checked you can use either the ip address or the mapped drive letter by selecting it from the file dialog associated with the trusted address function.
You may have to run Word as administrator in order to make this setting stick (although it shouldn't be necessary).
Meanwhile, refer to this official article
If you still have concern or problem after checking all the things above, could you please share with us screenshot of error message while you can't add the location as trusted location?
Let us know if you need further assistance.
Best Regards,
Waqas Muhammad