@Kwiatek 

Hi, 
If your network topology consists of a SIM card inserted into the Archer MR600 for internet access, and the UniFi controller (router) connected to the Archer MR600's LAN port for internet access, and your request is to disable the Archer MR600's router function, it cannot be fulfilled. In this case, the Archer MR600 needs to operate in 3G/4G wireless router mode. 

If your network topology is "an internet ethernet cable -- UniFi controller (router) -- Archer MR600", and you want to configure the MR600 as an access point (AP), please refer to the following instructions.
How to Set Up a TP-Link Router as an Access Point

Best Regards