Since 2010, I am IT Specialist at Purwodadi Botanical Gardens.
Here we need to think about (1) meaning and (2) form.
The word since means from a time in the past up to and including now.
If you mean up to and including now then you need one of these:
Since 2010 I have been an IT specialist at Purwodadi Botanical Gardens.
For 8 years I have been an IT specialist at Purwodadi Botanical Gardens.
I have repaired many computers.
In example (3) you are using present perfect to assure us that NOW (in the present) you are an experienced computer repair person, and we can trust you! We don’t need to know exactly when you did the repairs, or exactly how many computers you repaired – we just want to make sure that you are experienced!
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