How can I move the speed portal in the Geometry Dash editor?

It is possible to move speed portals only vertically.

According to the Wiki, it is possible to move speed portals only in the Y axis.

"Triggers and speed portals can only be moved vertically. Form portals' grids will not move with the portals, making it possible to make an offset of the grid."

This is probably because moving triggers and these portals would cause serious problems with soundtrack synchronization and gameplay testing in the editor, practice mode and even in normal play mode.

Sadly, there is not a way to move speed portals horizontally, at least not yet.

There are not a lot of times where you would want to change the X coordinate of a speed portal, because this messes up the rest of the levels sync. However, you can add the illusion of a "change of location" by placing down 2 of them, toggling one off, and adding some touchable trigger that toggles one on and the other off. Or another way to make them "move" would be like in Dear Nostalgists by Triaxis, where the rest of the level moves, and the Speed triggers stay in place, making them move across the screen at a different speed than everything else.

Hope this helps in whatever you were trying to do.