2nd Aorist Middle Voice

Compare:

Present Tense						Aorist Tense
I	arrive		ἀφικν	οῦμαι		I	arrived		ἀφῑκ	όμην
you	arrive		ἀφικν	εῖ / ῇ		you	arrived		ἀφίκ	ου
he	arrive		ἀφικν	εῖται		he	arrived		ἀφίκ	ετο
we	arrive		ἀφικν	ούμεθα		we	arrived		ἀφῑκ	όμεθα
you	arrive		ἀφικν	εῖσθε		you	arrived		ἀφίκ	εσθε
they	arrive		ἀφικν	οῦνται		they	arrived		ἀφίκ	οντο

  Note  

The aorist (simple past telling that somebody or something arrived, full stop), is actually easier than the present tense, which is contracted.
The temporal augment is a lengthened ῑ (with a macron to indicate lengthening of the vowel). Unfortunately I can't indicate the macron on a syllable carrying an acute, you just have to imagine it is there, invisible to the eye but audible to the ear.
The aorist stem of [ἀφικνέομαι] has lost the contracting νέ 
and has become purely and simply ἀφίκ 
The secondary endings are exactly the same as those of the imperfect middle voice we've seen before.

Another 2 past aorist middle forms:

τί ἐγένετο;     What happened?
πλούσιοι ἐγενόμεθα.  We became rich.
τί ἐγένου;    What became of you? [What did you become?]
μεγάλοι ἐγένοντο.    They grew big.