In Adventurers League play, DM's can receive rewards for the time that they spend DM'ing, that they can use for their own PCs:
Dungeon Master Quests are a series of out-of-game quests that DMs can undertake during the course of a specific season’s adventures. By completing quests such as DMing for a New player or logging a certain number of hours behind the screen, Dungeon Masters earn rewards for their own characters and their players. If you are an organizer, DM Quests are a great tool to recruit and thank your DMs.
So, DM Quests, can be awarded by event organizers, as an incentive and a reward for the DM's who are giving up their time.
One of those quest categories is called: Giving DM and it's awarded for having 'Run a game as part of a charity event'.
So, what does that mean?
A DM not being paid, does not make the game a charity game.
It is fair to assume that the majority of the time, the majority of DMs are not being paid for their work. They are doing it voluntarily.
This is the reason that the DM Quests exist in general - to help incentivise (and reward) people to give up their own time and DM for others for no personal gain. So, not being paid does not make any given game a 'charity event'.
What is a 'charity event' then?
Well there we can refer to the general understanding of this term - rather than a DnD specific understanding:
If you do something for charity, you do it in order to raise money for one or more charitable organizations. (Collins Dictionary)
And this seems to be the way that the DM Quests are using the term. Evidence of this can be found in the section of the Quest Sheet that details rewards:
DM's Reward: Double the standard DM Rewards. If the event is an Extra-Life event, also gain a Potion of Vitality for one of your tier appropriate characters.
Extra Life is a specific charitable effort, that is frequently supported by RPG players, which has raised more than $40 million for sick and injured kids since 2008.
So, a charity event, is an event (and in this context, one at which DnD occurs) which is specifically aimed at raising money for a charitable organisation or cause.
How could you get involved in a charity event?
If, as you say, no one in your country is running charitable events that you could volunteer to help with, then getting this DM Quest reward may prove tricky. However, given some time and effort, you might be able to organise your own event to raise money for a local organistation, or cause. Or, there might be charity events that you could support, and volunteer your time for, online.