Student or Learner
1."I think I saw you somewhere" is same as "I think I see you somewhere" ?
2.Can I use simple present instead of present perfect like above is used simple present instead of simple past ex-I have just got something in my eyes = I just have something in my eyes.?
1. No. They are different tenses so they have different meanings.
2. Both of your sentences are grammatically possible but they have different meanings.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.