PTo preventing the spread of infection at the office, young people were forced to move their working place from the 3rd floor to the 1st floor.

WAfter the move, we were often bothered by strange bugs appearing there.

To keep "appear" I might say: "After the move, strange bugs often appeared and bothered us."

The reason I removed "appearing" at the end of the original sentence is that it is implied by the bugs being there to bother you that they have already "appeared."

"Appeared" when used to talk about something or someone arriving or showing up gives off a feeling of being "sudden" or "abrupt" so I think it should come before "bothered" if you want to keep it.

I had never seen such strange bugs until I started working atin the suburbs.

On the other hand, there were a few merits.

Using "merits" works. Some other options I think fit slightly better are "benefits" or "positives."

For example, only young people could gather at the same place and safely discuss about something bad if they were heard of by senior peoplethings that we did not want the senior staff to hear.

The original sentence's meaning was quite unclear. My correction tries to change the sentence to align with what I think you're trying to say based on your Japanese sentence. My edits were more than just grammar, and if you want just grammar changes, the other users' corrections have done that (although the meaning is still somewhat unclear in those versions).

Some other options: "For example, young people could gather and discuss things that we did not want the senior staff to hear."

or "For example, young people could gather at the same place and discuss things without senior staff hearing."

or "For example, young people could gather at the same place and discuss things that would get us in trouble if the senior staff heard."

<Keywords>

This correction doesn't really matter, but since you have multiple words it might be better as "keywords."

PTo preventing the spread of infection at the office, young people were forced to move the working plair office from 3rd floor to 1st floor.

working place although technically correct is not a standard term

I had never seen such strange bugs until I started working atin the suburbs.

For regions, you are usually in them. I am in france, I am in the south, I am in the neighbourhood...

On the other hand, there were a few merbenefits.

For example, only young people could gather at the same place and discuss about something bad if they were heard of byby more senior people.

I do not really like my correction here. If someone else could give another phrasing, that would probably be useful.

PIn order to preventing the spread of infectionthe virus at the office, young people were forced to move the working place from the 3rd floor to the 1st floor.

I had never seen such strange bugs until I started working atin the suburbs.

For example, only young people could gather at the same place and discuss about something bad if they were heard of by senior people.

"Discuss" is immediately followed by the topic you're discussing. You don't need to write "about."