Glad you got it! I would just have ensured that I had separate workspaces on each screen - then a workplace switch would take you to the other monitor…
I would probably set them up with wmctrl - but then again I’m not on KDE, which may have a better way (and appears to by this thread)
I have heard that in some forum … but i don’t understand what does it means by have a separate workspaces on each screen… hence i didn’t bother. since you mentioned it, can you pls explain ? thx.
I am not sure how KDE arranges its workspaces, but essentially they are ‘viewports’ into the screen memory - enabling you to have different programs on each, uncluttered by the other programs you run. Perhaps, as an example, like this:
When you have a drop-down terminal defined that can pop up on any of them, that sort of setup simplifies life 
It would need some research to see how they are ‘arranged’ in KDE, they could be a conceptual:
line abreast:
or stacked by 2’s
or stacked vertically. Those apply to arrangements of 4 workspaces, which is common. The number is usually selectable in your settings somewhere.
A program like wmctrl can automate setting them up - or perhaps restore session would bring it back once you have it once - again - I don’t KDE
Hope this helps (or directs you in the right direction to investigate)
How about Alt+tab?