(suddenly, C is coming)
C : Hey, A, B what’s up?
B : Good morning C, today, A isn’t feeling well and I suggest him to go to the health unit, but he afraid he would be missing the math test
C : Oh I see, you should go to the health unit now and I’ll say to Mr. James that today you can’t follow the test because you’re sick
A : Okay, thanks, C.
B : Let us accompany you
(Then, they're going to the health unit)

can anyone help me to correct the mistake?
klingt das natürlich?

"Good morning C, today, A isn’t feeling well and I suggest him to go to the health unit, but he afraid he would be missing the math test"

This sentence is almost okay but there's a few things, I personally would move today to after "feeling well".
+ "Good morning C, A isn’t feeling well today"

Apart from that, it's mainly the tense that seems to be off, didn't you already suggest to A that he goes to the health unit? So I think suggest should be in past tense, suggested.
+ "A isn’t feeling well today, I suggested he goes to the health unit"

Again on the last part, "missing the math test". The math test hasn't begun yet so it should be future tense, miss.
+ "but he is afraid he would miss the math test"


Full sentence: "Good morning C, A isn’t feeling well today, I suggested he goes to the health unit but he is afraid he would miss the math test"
---

"Oh I see, you should go to the health unit now and I’ll say to Mr. James that today you can’t follow the test because you’re sick"

Only a slight adjustment to this sentence, again I would move "today" to after "test" and replace the word "follow" with "make"
+ "I’ll say to Mr. James that you can’t make the test today because you’re sick"

Follow doesn't really make sense here, make is good here because make can also mean "to arrive at or reach", so A cannot arrive at the test today.

Full sentence: "Oh I see, you should go to the health unit now and I’ll say to Mr. James that you can’t make the test today because you’re sick"