Front camera always dusty

Indeed that is possible; if you follow the front camera replacement guide, you will then have access to the inside of the screen glass and the camera lens itself so you can clean them both. iFixit doesn't have a guide to that procedure, but the Nadie Me Llama Gallina site out of Spain does.

Manuals / Samsung Galaxy A13 SM-A137 / Front camera - Nobody Calls Me Chicken

Of course the site is in Spanish, but used in conjunction with the Chrome browser's translation feature, it is quite usable and well done.

Note that this is for the SM-A137 rather than the SM-A135 that the device page you selected indicates, but I suspect the phones are similar enough that you will be able to get through it.

Take lots of pictures as you work and once you're done you can use them to create your very own iFixit guide to that repair! It's easy, fun and the repair community will appreciate your efforts!

Good luck, and let us know how it all turns out in any case.