After giving CRTLF command, You will find the options for entering Logical file Name and the Library name where you want to create LF.
Ather those fields You will find the fields under ‘Physical file data members’ saying Physical File Name, Library Name where physical file exist and the Member Name.
You can give the Member Name of a Multimember PF at Member name option.
Specifically, the DTAMBRS keyword:
DTAMBRS((PF_LIB/PF_NAME (MBR_NAME MBR_NAME2)))