How to bid for an EVA Air upgrade seat?
If you want to choose the bidding route to make the Eva Air Upgrade, you have two options. First, you will receive an invitation to bid by default from the airline’s side in the email you provided. You can make your bid on that. Secondly, if you cannot wait & want to ensure an upgrade, you can do it yourself:
Visit the EVA Air official website.
From there, head to the EVA Bid Deal page to make the bidding request. 
Select the “I am interested” option to check your upgrade availability. 
Choose a price & share your payment details.
Submit an offer. 
If your bidding is accepted, you will be charged the bid amount. 
For more information you can contact EVA Air customer service or you can also read the blog by Airlines Group Travel at the mentioned link.

Read more:- https://www.airlinesgrouptravel.com/blog/how-to-upgrade-on-eva-air