In reply to abhi9891:
As Dave mentioned, it would be very beneficial to post a complete example which demonstrates your issue.
The following code works in all simulators on EDA Playground:
module xyz();
logic \signal_a[0][0] ;
endmodule
module top;
xyz i_xyz();
initial begin
force i_xyz.\signal_a[0][0] = 1'b0;
end
endmodule