After completing the first mission with Major Sweetie, you have to find three items of Cool Swag for the Lawnmower. This quest will have you collect the Cool Bling item for the Lawnmower. To start, find Tenderleaf the Acorn on the map. Complete the quest and the achievement should unlock.
*** Spoiler - click to reveal ***
Tenderleaf's squad ran into trouble looking for Treasure Yeti and his Bling. You have to rescue the Acorns and obtain his Cool Bling.
Go to each objective to find the trapped acorns. In each objective, a control panel is required but the Treasure Yeti has taken it. Attack the Yeti until he drops it. Pick it up, return back to the trapped Acorn to set it free and destroy the panel. Each objective has something different after rescuing the Acorns.
For the first one, simply protect the Acorn.
For the second one, follow the Acorn to find a Shiny Lore to help you on the third rescue. The Lore will be a shiny boot.
For the third rescue after placing the lure, defeating the yeti, and rescuing the third Acorn, you have to escort the Acorn to safety.
Once all three Acorns are rescued, the Yeti will show up to ruin the party, but the Acorns have a little surprise up in their sleeves. After the cutscene, the quest will end and you will have your achievement and Cool Bling item.