Please help me.
I want to write a lisp command "MVIEW". Like youtube video.
I fail to see why this is so desperate for you - it is only a speed up of what you can carry out anyway - just do it manually.
MVIEW is a native AutoCAd command - read the help on it if you are unsure.
Just make sure you are in paperspace, and on the layer you want your viewport to exist (usually non-printing), then issue the MVIEW command.
Pick points for the corners of the viewport and you get the whole drawing visible in the viewport. Double click on the viewport to get into modelspace and set the scale for printing - e.g. command ZOOM, then set scale at prompt such as 1/50XP, pan to get the view you want - and return to modelspace. This would give you a viewport on your sheet at a scale of 1/50 when the sheet is printed full size - the XP suffix does that. If you need to resize the viewport, click on it and then Grip-edit it.
No one is going to write you a lisp for what you want - why is it so important?
Please understand, this is a user help forum not a free code generation studio. You are unlikely to get somebody to write wholesale functions on demand. If you have created some code, and are stuck on some flow logic or syntax, posters may provide some assistance. But the level of assistance you seem to be expecting is unlikely to come through repeated demands of "help me".
If you are going to fly by the seat of your pants, expect friction burns.
Adopt. Adapt. Overcome. Or be overcome.
The sad thing is that the program requested is actually slower and more complicated than the method Gordon explained. See video. In contrast to the over 5 minute process demonstrated on youTube, this method takes less than 2 minutes and accomplishes the same thing. After doing this, if you want the layout to be back in model space, just export it.