Use $sformatfLRM section 21.3.3 Formatting data to a string to create the string with the correct hdl path, btw I recommend to first check if the path exists or if the force was successful
for(int i=0; i<8; i++) begin
for(int j=0; j<8; j++) begin
uvm_hdl_force($sformatf("DUt.abc.pkt.reg_%0d.w[%0d]",i,j) , data);
end
end