Export from Trello and import to Upwave is done at the board level.
Export from Trello
Information on how to export from Trello is found on their helpdesk. In Trello, go to Board Menu > More > Print and Export. Save your board(s) in your download folder.
Import to Upwave
From your Upwave dashboard, go to the teams tab and select the team where you want the imported board to be placed.
1.Go to the team where you want to put the board, click on the three dots next to the team name and select "Import board".
2. Select the board you want to import from your download folder (<board>.json)
3. Click the “Start import” button, located bottom left within the pop-up frame
Voilà, you are all done! "Board has been imported!" will show, click “Goto the board” and review the board.
After you have navigated around and checked your data, you can either import more boards, invite collaborators, or just start working.