MIB Additions

I would like to know if someone could explain to me how to go about adding MIB files and what needs to be done as far as the .yaml file is concerned. We have several Fortinet (formerly MERU) wireless controllers in our network which I’d like to get the SNMP statistics for, I’ve downloaded the MIB files from the controllers and most of the MIB files still say MERU on them, what procedure do I need to take to be able to use these?