Position the cursor in a cell directly below the row break indicated by a horizontal line and choose Sheet - Delete Page Break - Row Break. The manual row break is removed.
བཀའ་ཚིག་ལ་བཅར་འདྲི་...
From the menu bar:
Choose Sheet - Delete Page Break - Row Break.
From the tabbed interface:
On the Layout menu of the Layout tab, choose Row Break.