You cannot just upload a MIB file somewhere and magically get new checks from that content.
The MIB only defines names for object IDs and sometimes mappings from integers to states or other meanings. But there is no syntax in the MIB that a computer can use to interpret the values.
This has to be done by a human author writing the SNMP check plugin.
See section 4 of the legacy documentation https://checkmk.com/cms_legacy_documentation.html as starting point and continue to read available check plugins.