Errors:  

 "have seen advertisement" should be "have seen an advertisement."

"news paper" should be "newspaper."

"a delivery master post" should be "the delivery master position."

Corrected version:

I am writing this letter to apply for a job in your post office, as I have seen an advertisement in the newspaper regarding the delivery master position.

Improved version:

I am writing to apply for the delivery master position at your post office, as advertised in the newspaper.

Errors:  

"graduation in technology" should be "degree in technology."

"last month" is not necessary as it is understood.

Corrected version:

My name is Shalini, and I have completed my degree in technology.

Improved version:

My name is Shalini, and I have recently graduated with a degree in technology.

Errors:  

"local area" should be "the local area."

"local language" should be "the local language."

"help to communicate" should be "help me communicate."

"native people" can be better phrased.

Corrected version:

Moreover, I am familiar with the local area and the local language, which will help me communicate with the residents.

Improved version:

Furthermore, I am well-acquainted with the local area and fluent in the local language, facilitating effective communication with the community.

Errors:  

"well-interested" should be "very interested."

"blue dart Company" should be "Blue Dart company."

"there I was engaged" should be "where I was engaged."

"delivering courier" should be "delivering couriers."

"labelling job" is unclear and needs rephrasing.

Corrected version:

Furthermore, I am very interested in courier work as, during my school days, I worked with Blue Dart company, where I was engaged in picking up and delivering couriers and handling labeling tasks.

Improved version:

Additionally, I have a strong interest in courier work, having previously worked with Blue Dart during my school days, where I handled picking up and delivering packages as well as labeling tasks.

Errors:  

"wants" should be "want."

"in future" should be "in the future."

"helps" should be "help."

"fullfilling" should be "fulfill."

Corrected version:

I also want to start my own courier company in the future, so this job will help me a lot. Apart from this, I have some financial issues too, so the money I earn will help me fulfill my basic needs.

Improved version:

I aspire to start my own courier company in the future, and this job will provide valuable experience. Additionally, the income will assist in addressing my financial needs.

Errors:  

"Hoping" should be "I hope."

"some positive response" should be "a positive response."

Corrected version:

I hope to get a positive response.

Improved version:

I look forward to your positive response.

Errors:  

"Your’s" should be "Yours."

The closing should be aligned properly.

Corrected version:

Yours faithfully,

Shalini Rana

To,

The Manager,

Respected Sir,

I am writing to apply for the delivery master position at your post office, as advertised in the newspaper.

My name is Shalini, and I recently graduated with a degree in technology. Furthermore, I am well-acquainted with the local area and fluent in the local language, facilitating effective communication with the community. Additionally, I have a strong interest in courier work, having previously worked with Blue Dart during my school days, where I handled picking up and delivering packages as well as labeling tasks.

I aspire to start my own courier company in the future, and this job will provide valuable experience. Additionally, the income will assist in addressing my financial needs.

I look forward to your positive response.

Yours faithfully,  

Shalini Rana