Correct spelling, explanation: this word is a merge of the verb submit and the ending -ing. It was created the right way, with the double -t letter. It’s the only correct spelling, because – according to an important principle – the last (and stressed as well) consonant in a derivative must be doubled if there’s a single vowel before it. You must write down this word as submitting, not submiting.

Definition of submitting:
noun (gerund), presenting or referring to others for decision, consideration
Submitting your application before February 16th is a necessary condition.
When will be the deadline for submitting documents?

Collocations with submitting:
Some most commonly used collocations include: submit evidence, and submit a proposal.
You will be asked to submit further written evidence to back up your claim.
Since submitting the original proposal, some modifications have been made.

Incorrect spelling, explanation: the right form of this word – submitting – is a derivative of the verb submit. Present participles of English verbs are always formed with the suffix -ing. In this case, we also need to double the -t letter due to the important principle: when there is a single vowel before the last, stressed consonant in a word, we need to double that consonant. Therefore, submiting is not the correct version.