I made a donation of clothing earlier this year and now have more to add. how do i add a new donation with a new date?

2019?

yes

Go to whatever year you want to add the donation. Click visit. Go to items, click edit. Below the totals of what you already have entered, click on add item donation. Choose or add your new charity and input your date.  Then, "rock on." From your bookkeeping standpoint, it's better to keep things separate.