Consider the scenario of FIFA 2018 with 4 teams in semi finals: France, Belgium, Croatia, and England. In this scenario every team is equally likely to win the World Cup, so the probability that a given team wins is 1/4.
Now France has qualified for Finals, has their chance increased to 1/2? Or, just like Monty hall problem, is it that every team has 1/3 chance to win world cup?
How do I solve this problem?
You have assumed, but not stated the assumption, that each team in a game has $\frac 12$ chance to win. Now that France has qualified they only have to win one game to win the cup, so their chance is $\frac 12$. Whoever they beat now has $0$ chance to win. The other two teams are in the same position they were-they need to win two games, so have $(\frac 12)^2=\frac 14$ chance to win overall.