I too am in this episode

It's from the short "Christmas: Cold and Fast" from the holiday anthology Tis The Season To Be Freezin'

On an unseasonably warm evening before Christmas, Len is ringing a bell dressed as Santa on a street corner calling for donations to help the less fortunate. A Banker Type makes fun of him, and Len steals his watch, but Barry zips in to take it.

The two squabble, Barry questioning whether any of the money is going to anyone who actually needs it, and Len explains that he was going to use it to hire some people to help him with something. He (after arguing back and forth over it for almost a whole page) convinces Barry to open a truck...

Which is filled with toys.

Len was originally going to sell them all, but he decided instead to give them to kids in need.

Barry then asks Len to give the people of Central City a Christmas miracle

by freezing the ice rink for the tree lighting ceremony.

Len agrees on one condition...

That Barry wears his Santa suit.

Barry races around Central delivering toys (Pretty much all Flash themed, which makes me wonder if he keeps a warehouse of his own merch...), then they meet up on top of a building to watch people skate.

(Yes, Len just jumped off the roof of five storey building. What a dramatic little shit.)