Errors:  

"going for urgent office work" should be "going away for urgent office work."

The sentence should be split into two for clarity.

"I want to thank you for this" is slightly informal.

Corrected version:

I am glad that you agreed to stay at my apartment while I am going away for urgent office work. I want to thank you for this.

Improved version:

I appreciate that you agreed to stay at my apartment while I am away for urgent office work.

Errors:  

"Moreover" can be replaced with a simpler transition.

"Give you some information" is slightly informal.

Corrected version:

Additionally, I would like to provide you with some information about my apartment as you are visiting for the first time.

Improved version:

Furthermore, I would like to offer some details about my apartment since it is your first visit.

Errors:  

"In sector 12" should be "in Sector 12."

"The market is near" should be "The market is nearby."

"Any grocery" should be "any groceries."

Corrected version:

My apartment is located in Noida in Sector 12. The market is nearby if you want to purchase any groceries for yourself.

Improved version:

My apartment is located in Noida, Sector 12. There is a nearby market where you can purchase any groceries you need.

Errors:  

"Further" should be replaced with "Furthermore" for formality.

The comma should be a period to separate the sentences.

"Roof top" should be "rooftop."

Corrected version:

Furthermore, my apartment is very spacious. It has three rooms along with a rooftop garden.

Improved version:

Moreover, my apartment is quite spacious, featuring three rooms and a rooftop garden.

Errors:  

"AC of master bedroom" should be "The AC in the master bedroom."

"Electric issue" should be "electrical issue."

Corrected version:

The AC in the master bedroom has some electrical issue, so please operate it carefully.

Improved version:

The AC in the master bedroom has an electrical issue, so please use it cautiously.

Errors:  

"Apart from this" can be more formally phrased.

"Water them on regular basis" should be "water them on a regular basis."

Corrected version:

Additionally, please take care of the plants and water them on a regular basis.

Improved version:

Additionally, please tend to the plants and ensure they are watered regularly.

Errors:  

"I also left" can be more smoothly integrated.

Corrected version:

I have also left a welcome gift for you in the wardrobe.

Improved version:

I have left a welcome gift for you in the wardrobe.

Errors:  

On my alternative number" should be "on my alternate number."

"Neighbour aunt (Marie)" should be "my neighbor, Aunt Marie."

Corrected version:

In case of any emergency, you can call me on my alternate number or you can also seek help from my neighbor, Aunt Marie.

Improved version:

In case of an emergency, you can reach me on my alternate number or seek assistance from my neighbor, Aunt Marie.

Errors:  

"Switch off" should be "turn off."

"My alternative number" should be "My alternate number."

Corrected version:

I have to turn off my personal number due to work. My alternate number is 237-462-367.

Improved version:

I will need to turn off my personal phone due to work. My alternate number is 237-462-367.

Errors:  

"Thanks" should be "Thank you."

Corrected version:

Thank you once again for the help.

Improved version:

Thank you once again for your assistance.

Errors:  

"your friend" should be "Your friend."

Corrected version:

Your friend,

Shalini

Dear Amit,

I appreciate that you agreed to stay at my apartment while I am away for urgent office work. Thank you very much.

Furthermore, I would like to offer some details about my apartment since it is your first visit. My apartment is located in Noida, Sector 12. There is a nearby market where you can purchase any groceries you need. Moreover, my apartment is quite spacious, featuring three rooms and a rooftop garden. The AC in the master bedroom has an electrical issue, so please use it cautiously. Additionally, please tend to the plants and ensure they are watered regularly. I have left a welcome gift for you in the wardrobe.

In case of an emergency, you can reach me on my alternate number or seek assistance from my neighbor, Aunt Marie. I will need to turn off my personal phone due to work. My alternate number is 237-462-367.

Thank you once again for your assistance.

Your friend,  

Shalini