Hi Chukwudalu,
welcome to our Dlubal Community 
We are very glad to have you here!
Generally: Lines that are integrated into surfaces create a constraint for the meshing algorithm. Hence, it may help to add some additional lines into the surface.
Specifically: If you have a specific issue with a model, please share it (without results) so I can take a closer look.
In RFEM 5 it is not possible to adjust the mesh coordinates manually.