Are you trying to connect the MHF4 plug to the EM7455 receptacle or a micro coaxial cable to the plug?
The RF receptacles on the EM7455 are not designed to be soldered, so soldering directly to these receptacles is not advised. These connectors are push fit but can be a little difficult to connect, you need to make sure the plug is properly aligned and square with the receptacle before pushing down on the top of the plug. These small plugs can get damaged very easily. You may want to double check that the plug and receptacle has not been damaged. IPEX also make a tool for connecting and disconnecting the plug to and from the receptacles. It may be worth investing in one of these tools.
It is recommended that you Use RF plug connectors that are compatible with the following RF receptacle connectors: Foxconn (KK12011-02-7H), Longwell (911-002-0006R), Speedtech
(C87P101-00001-H), Murata (MM4829-2702RA4 (HSC)), IPEX (20449-001E