A: I prepared for the meeting materials.

or

I prepared the material for the meeting.

First, I listed up what I needed.

Then, I did a quick search in the shared folder for related materials(s).

Finally, I arranged thea meeting with the person whom may Iit concerned.

That's what I did in the morning.

A: I prepared materials for thea meeting materials.

Unless person Q already knows about the meeting, you have to use 'a' and not 'the'.

First, I listed upout what I needed.

you:
list out

but you:
write down

unless it's a long document and then you:
write up

Fun isn't it?

Finally, I arranged a time for the meeting with the person whom may I concerned I am presenting to.

I speak and write American English and we almost never use `whom`, instead we usually use `who` unless it is a formal situation.

That's what I did in the morning.

First, I listed up what I needed.

No need for 'up', here, because 'listed' is not a phrasal verb. 'Need' should be in the past tense, like the other verbs in your writing.

Finally, I arranged the meetinga time with the person whom may I concerned I am going to meet.

Use 'a time' here to avoid repetition, i.e. .so you don't have two 'meet' words in the same sentence (sylistic).
'To whom it is concerned' is a way to start an email or letter, but not really something we change or use in other ways in writing. Instead, use a defining relative clause with 'who' to specify or identify the person you are talking about (i.e. Q: Who did you arrange the time with? A: The person [who] I am going to meet).

That's what I did in the morning.

Think about the original question: 'What did you do in the morning?' Here, you are repeating ('reporting') the original question, so use 'what' as it appeared in that question.