can you show me the concrete code after modification?

Sure, here is the modified code with the fixes applied:

module inner_submod (input logic [9:-1][2:0] sub_input, output logic [9:-1][2:0] sub_output);

    assign sub_output = sub_input + 1;

endmodule

module test_top;

    typedef struct packed {
        logic [9:-1][2:0] a;
    } ST1;

    typedef packed struct {
        ST1 st1;
        ST1 st2[2:0];
    } ST2;

    inner_submod submod1 (
        .sub_input(st2.st2[0].a),
        .sub_output(st2.st2[0].a)
    );

    inner_submod submod2 (
        .sub_input(st2.st2[0].a),
        .sub_output(st2.st2[0].a)
    );

    inner_submod submod3 (
        .sub_input(st2.st2[1].a),
        .sub_output(st2.st2[1].a)
    );

    initial begin
        ST2 st2 = '{ 2'b01, {3'b1, 3'b0, 12'b1} };
        $display("st2:%s", st2);
    end

endmodule

Note that I have added the module "inner_submod" and its input/output ports to the first module declaration, and I have also added semicolons at the end of each inner_submod instantiation.