As @Idolenz says it is not so easy.
His method is probably the best, I tried it here now:

To get the actual sequence of the arabic letters, I used this page:
Arabic Keyboard Online • Lexilogos
To get that exact sequence, I typed in this order (using their virtual keyboard).
The main numeric sequence (you type this as normal, left to right):

Next is the alphanumeric, which includes the space, the arabic letter and the slash. These you type from right to left:

Last, is the three numbers in the prefix. These you type normally from left to right:

The thing to do now is not to try to highlight the final entry with your mouse and press CTRL-C, you use the “Copy” button on that page

You can then paste that here.
٨٢٢١٩٤٦ م/٣٣٢