Dear Zenchao,
your question is actually two questions in one.
Q1: to convert gmsh mesh to ogs either you can use the tool provided form OGS (see this question ), or you can prepare a script (see this python script to have an idea what to do, please note this script is extremely not optimized )
Q2: did you try to compile the OpenGeoSys? did you manage to run a similar problem (for example Non-isothermal test )?