The second one.
There are 2 kinds of Alif with Hamza : أ and إ
The first one أ is when you have a Fat'ha or a Dhamma sound.
The second one إ is when you have a Kasra sound.
Here we have the word إعتمر (pronounced : i-itamara), starts with an Alif with Kasra sound, so it must be written like إ
Hello, I am actually not agree with the answer of Sleem. The verb must comes with ا with no hamza. There are no such word coming with إ or أ with that verb.
The good one should be:
اعْتَمَرَ
I advice you to look at an Arabic dictionary named: معجم الطلاب to give me more details about that. Thanks for being understood.
السلام عليكم ورحمة الله