"During the first year"is correct. "first year" means a definite time ,so indefinite article 'a' is not suitable here.
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Nancy1982During a (if this is part of an article where you're usually talking about a future plan that will be used or might be used, its better to use "the" because you're specifyeing that this plan is for "the" first year) first year, a (this rule is also applied here, so if you've specifyed which fees are goining to be involved in the plan you have to use "th