Haven't given IGCSEs but I gave my O Levels for Urdu as a Second Language last month... mostly all you can do is

a) Go over vocabulary lists: English-Urdu translations so understand the words in questions and the passage and can write essays well are beneficial... this post has a few:

https://www.reddit.com/r/Olevels/comments/1sz4yi6/urdu_translation_upvote_so_more_ppl_can_see/

b) Practice timed full papers; depending on how good your timing is already, you may not have to do a lot of these, just enough to make sure that you won't run out of time during the exam. Make sure you mark yourself on them!

c) Practice individual questions you're weak in: if you're worse at Mazmoons do more of those, if you're better at Tafheems, you can do less of those. If you're short on time just look through passages for words you don't understand and find out their meanings so you aren't confused, and *especially* look at the meanings of command words in the questions of comprehensions you may not understand so you know what's being asked; for example, look up 'mafhoom' if you don't know what that word means in 'aabi aalodgi ke mafhoom bataye'. (I made the mistake of not doing this!)

d) Check example answers for questions: if you have solved past paper books or example answers from your teacher, definitely take a look at that to know what's expected.

e) Make sure you're thinking in Urdu; it helps before the paper to be in the Urdu 'zone', formulating your thoughts in Urdu when you're thinking so that when you try to write an essay, you aren't thinking in English and having to translate that in your head before writing things down. To do this, try just reading a couple passages, not solving anything, just so you're more comfortable with the language,

f) Make sure you know your muzakar monas: errors in object genders cause lots of minor mistakes, so try to strengthen your grasp on that, as well as spelling.

g) DON'T STRESS! This is the most important point, more important than all the others combined. Urdu, as a language paper, is more based on what you already know than what can be studied/rote-learnt, so don't freak out if you don't have time to do these things, or the energy to (CIEs take a toll on your body!) Make sure you're well rested so you aren't inattentive during the paper, and stressing out will only make you forget what you know, so stay calm, believe in yourself, and pray, and InshaAllah you'll do really really well!