Aside from adding a couple of new playable characters, the Dragon Ball Xenoverse 2 DLC Pack 1 brought new Parallel Quests (PQs) --- the first two of which allows players to unlock Champa's and Cabba's clothes.

Unlocking Champa's Clothes

First off, you must have DLC pack 1 to initiate the quest. Unlocking Champa's clothes is quite straightforward as all you need to do is complete the Parallel Quest #101 dubbed as "Seeking Fighters for Tournament!"

Win Condition(s) for the quest include the following:

Wipe out all enemies.

Lose Conditions:

All team HP used up.
Goku and Vegeta are destroyed.
Time limit expires.

It is worth noting that the quest in itself is not arduous as the enemy bosses do not mete out a lot of damage. However, the catch in here is that you are putting up a fight against time. You have less than 15 minutes to beat all of the bosses in this quest.

In order to get your hands on the clothes as quickly as possible, it is suggested that you bring a couple of friends for this event. That being said, you can also solo this event by using characters that dish out high damage with their Ki moves, for instance, Metal Cooler. All you need to do is deliver your Super Nova on the enemy bosses and you are all set to go, according to iTechPost.

There is a possibility that unlike other rewards dropped via Parallel Quests, this quest may not drop a piece of Champa's clothes. Basically, in order to fully unlock Champa's outfit, you will need to work really hard on the quest. Take a look at a video footage posted on SaiyanIsland showing exactly how you can acquire Champa's clothes.

Dragon Ball Xenoverse 2 DLC Pack 1 has been rolled out worldwide, except on PS4 and Steam in the United States.