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1. If the noun or the adjective before the noun starts with a vowel sound (not a letter, but a sound), we should use the article 'an'. Vowels are 'AEIOU'. We need "a" with "BPO". We cannot use "an" before the consonant sound "B".
2. We use the definite article "the" in front of a noun when we believe the listener/reader knows exactly which specific noun we are referring to. You're referring to a specific noun, specific 'help desk', so we need the definite article 'the' here.
3. "As such" is not usually used here. We could use "in my line of work", to explain what happens there, or we could use "therefore" or "hence" to show consequences or results.
4. We must use singular verbs with singular subjects and plural verbs with plural subjects. If a subject is singular (for example, "cat"), the verb must be singular too (for example, "plays"), and if a subject is plural, the verb must be plural too (cars have; people go). Subject-verb agreement refers to the agreement or harmony between the subject (the person, thing, or concept that performs the action) and the verb (the action or state of being) in a sentence. It means that the form of the verb must match the form of the subject in terms of number and person. Remembering and applying subject-verb agreement rules helps ensure that sentences are grammatically correct and sound natural.
5. We need an object to explain who receives questions from customers. We could use "me".
6. "And" should not be used here because "and so on" was used at the end. We need a comma.
7. The sentence "I am an agent of IT help desk. Hence, customers asks about networks, PCs and devices and so on." is almost identical to the previous sentence, except for the phrase "hence" which was used instead of "as such". Correction 3 provides an explanation about what phrase should be used here, so this sentence is not required. And the rest of the corrections are identical as well.

1. "One" is not required here. We only need the adjective to describe the subject.
2. The comma is not required here.
3. We use the definite article "the" in front of a noun when we believe the listener/reader knows exactly which specific noun we are referring to. You're referring to a specific noun, specific 'atmosphere ', so we need the definite article 'the' here.
4. "Moreover" is usually written as one word.

1. You expressed yourself well here. There is nothing to correct, so this is an alternative expression we could use in this context - "However, other departments cater to clients from abroad."

1. "Most" should be followed by a plural noun and we need the comma after the introductory phrase "in most cases".

1. You expressed yourself well here. There is nothing to correct, so this is an alternative expression we could use in this context - "I suppose there has been a slight increase in the number of employees."