Work as a Ssteward inat the 2018 FIFA World Cup in Russia

The sporting event I have witnessed iwas the 2018 FIFA World Cup - an international football tournament.

It happened in Russia, and some games were in Moscow, where I lived.

Alternative: "It took place in Russia..."

I used to worked as a Ssteward and participated in a gamt the Belgium versus. Tunisia game.

"Used to" would imply that you weren't working at the time of the Cup.
"Participated in a game" = played in the game.

I was not interested in a football, but this event was a tipping point in my attitude to this competition.

Alternative: "this event changed my mind" or "this event made me see things differently"

"A football" = a physical ball (soccer ball in the US)
"Football" (uncountable) = the game (soccer in the US)

Furthermore, I can still remember the public's excitement that the public was sharing, it stays in my heartas if it were yesterday.

What you wrote is grammatically correct, but it sounds a bit unnatural.
"as if it were yesterday" is a great collocation to use here.
You could also say "I remember it vividly."

The audience was fanaticcrazy about that game.

"Fanatic" is pretty much only used in terms of religious fanaticism

https://stanfordmag.org/contents/fan-or-fanatic

I stood next to them with the fans from Tunisia and watched them - it was my job.

They screamed and cried whenever someone scored a goal.

What you wrote is correct, but this sounds slightly better to me.

The whole stadium was filled with joy, and happiness.

The players gave the same energy back to the crowd.

After the game we shared with colleges our thoughts about that day, my colleagues and I shared our thoughts and discussed the most interesting moments inof that worke day.

EventualShortly after that, I started to engage in football life.

"Eventually after that" sounds quite odd to me. The collocation is usually "shortly after that" or "soon after that." If it wasn't shortly, you could just say, "Eventually, I started..."