To use instant trade  navigate to your trade section in the Bunt app. 

From here select the cards that you would like to trade: 
Once an eligible set has been selected for instant trade, a variant will also need to be selected. By selecting the first card in the trade from your binder, the rest will automatically filter down to only cards from that variant. To back up and select a different variant, simply deselect all cards from the trade table. 
 
Once you selected the card(s) you would like to trade you press done 

Then BuntBot will then populate cards from the set and variant that you are eligible to receive.  
Chose from this list of eligible cards the player and variant you need to complete the set. 
After the cards are selected press send. 
You have then successfully traded with Bunt Bot for instant trades.