You just need two APN Settings for differ LTE module and it’s all for have 2 connections.
Of course use latest RouterOS bcs some old version have some bugs to use both lte interfaces together.
To using 2 connection and do LB etc. it’s differ story. MultiWan in my fav way: http://forum.mikrotik.com/t/moving-from-fail-over-to-using-both-wans/143145/2 .