Steps
Open Assessment → Activity Board.
Find the card. Tick Mine only to narrow the board to your own work.
Drag the card to the next column. (Or click it and use a Move to … button in the right-hand panel.)
If Conform asks for a rationale, say why you're moving it, for example "Controls confirmed; scores reviewed with the area manager".
If asked, choose who picks it up next. The list only shows people who can work in that stage.
Click Move. The card lands in its new column.

Moving a card to Completed finishes the assessment for this cycle. After a few days it goes to the Forward-Log, and comes back to the Back-Log when it's next due.
If you can't drop it
A column shows as locked when your workflow roles don't allow that move. Ask whoever manages your workflow roles; see Workflow roles.