Hi sharul,
Sorry to say that iFixit doesn't have the guides you need to fix your phone; as much as they'd like to they're only human and can't be everything everywhere all at once. However, there is a Spanish site called Nadie Me Llama Gallina that has just what you need to replace those speakers. Here are the guides you'll want to follow.
[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/samsung-4/samsung-galaxy-a13-sm-a137-1378/altavoz-buzzer-12477|Manuals / Samsung Galaxy A13 SM-A137 / Buzzer speaker|new_window=true]
[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/samsung-4/samsung-galaxy-a13-sm-a137-1378/auricular-12478|Manuales / Samsung Galaxy A13 SM-A137 / Auricular|new_window=true]
Note that the A13 comes in a couple of different models; the device you've filed your question under is the SM-A135 while these guides are for the SM-A137, but hopefully the differences are minor and they'll get you through your repair; just be prepared that some small things might not be exactly the same and use common sense to figure it out.
As far as finding the parts, I don't think it will be too difficult; I usually start with the big three; Amazon, eBay and AliExpress. Do your search using Galaxy A13 but try to confirm the part with your actual model number.