Staves spacing question

Hello! In this example, attached, I would very much like that the first stave on page 6 will be included in page 5 and start page 6 with the new flow. As I made lots of space for it, how can I make the staff go to the previous page?
And an extra question, once it does go to the previous page, as it should, the last three bars (78-80) are a bit empty to justify a whole line. Is the any way to make these bars end half-way into the page?
Many thanks!

Dragging staves manually in Dorico will never result in it automatically moving staves onto different pages.
In Engrave mode, select the first thing you want on the page (such as the multi bar rest at bar 40), then Ctrl/Cmd click the the double barline at the end of the flow, then hit the Make Into System button in the left panel.

To handle this globally go to Layout Options > Vertical Spacing, make sure you have the correct layout selected in the right column and then reduce the Gap Between Systems.

The global setting for whether final systems should spread across the page is at Layout Options > Note Spacing (it’s the final option on that page).
Locally you can do it by going into the Note Spacing submode of Engrave mode, selecting the big square handle above the final barline and then using Alt/Opt-Left arrow (add Ctrl/Cmd for bigger steps).

Thank you so much for the amazing help, as always!