i played once in tournament and i beated 1700 elo rating player but then i lost to average 1400 and then i won to 1800 elo rating whats the tool to determine my exact elo rating cause im confused
The elo system (and glicko one that chess.com uses) are simply estimates to your rating. Plus, it all depends on your rating pool. Chess.com 1000 rating is not identical to USCF 1000 and not identical to FIDE 1000 and so forth. Think of it this way, what if you played the same person in chess - day after day - and always lost. Your rating may be very low, but it is also possible that you are a strong chess player and that your opponent day after day was actually a GM! Ratings (chess or something else) can never be exact, but they can become more accurate with a larger sample size.
If you want to know you approximate rating on chess.com, then play more games on chess.com - same with any other category, rating pool, or rating system you use.
Finally, humans are not machines that play at their own ability every day. It is normal for a human play to win against someone a few hundred points higher rated than them and then lose to someone equally lower rated than you: they simply balance around your rating. The fact that you can win against a 1700 or 1800, yet lose to a 1400 just means you are human and have good and bad days like the rest of us. 
Who knows, maybe that 1400 play you lost to shouldn't really be 1400. Perhaps they are on the way up and really 1800-level. All you can do, is play your best and the numbers will balance themselves.
i played once in tournament and i beated 1700 elo rating player but then i lost to average 1400 and then i won to 1800 elo rating whats the tool to determine my exact elo rating cause im confused