Yáʼátʼééh! This is called the durative imperfective mode (the aspect and mode can occur in the verb), and it can be used for the imperative form, in the second person. This conjugation can be also called distributive plural:
The imperfective indicates an event/action that has begun but remains incomplete. Although this mode does not refer to tense, it is usually translated into English as a present tense form: yishááh "I'm (in the act of) going/coming", yishą́ "I'm (in the act of) eating (something)". With the additional of adverbials, the imperfective can be used for events/actions in the past, present, or future. The mode is used in the second person for immediate imperatives.
I think this is the spelling in Wiktionary:
Edit: Also, there is a form without the glottal stop: