I'm a newcomer into this forum.
Who can tell me the different between Eventually and overtime?
I think you mean "over time," and not "overtime." The words "eventually" and "over time" have a similar meaning, and in some sentences you could use either.
"Eventually" means "in the end" and can have an idea of "after difficulty:" "He studied English for 5 years, and found it very difficult, but eventually he became very fluent." It can also mean "in the end, after delays, later than you'd like: "Their son eventually moved out of the family home at the age of 30."
"Over time" stresses the duration / length of time, rather than the end: "I'm studying English vocabulary every day, and over time I've learned a lot of words." There's no idea of difficulty / delay / expectation with "over time" as there is with "eventually."
(There is also a word "overtime" which means the time that you work at a job longer than the usual number of hours, and in some jobs you get paid extra for this: "She earned lots of money working overtime." "The business failed because it had to pay too much overtime to its stressed workers.")