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