Possibly with Interest
On Return Something You Borrowed Day, you get to make nice with someone - whether you like each other or not.
It is suggested that, especially if you don't care all that much for each other, you include something a little extra in your repayment.
What you return can be either a consumable or a non-consumable, like a piece of hardware. Did you borrow a rake that's still standing in your garage? Clean it and give it back. Did you borrow the proverbial cup of sugar? Measure out a cup and a half or even two full cups.
If you really can't think of anything you need to return, you could stretch it a little and say you want to "return" a hug or a kiss or some other act of kindness that was done for you once upon a time.
Let's keep the terminology straight in all this, though.
The other person did not borrow you something. They loaned or lent you something.
You borrowed it from them.
That reminds me. It's "on purpose" and "by accident" - not "on accident".
I feel better now.