how i can open a file in assembly language

From the Language menu, select A and then Assembly. That will enable syntax highlighting for the assembler opcodes.

Now from the File menu, select Open, browse to where your .asm file is stored and click the Open Button.

That will open the file in a new tab.

Before you edit it, you might want to save it to a new file (File ->Save As) so you can revert to the original file if you mess up.