What pocococo said. But if you haven't gotten the spell yet (I can't remember if it's already in your spellbook), you can also use the hackmover cheat.
To enable cheats, you need to start the games with an additional parameter.
For The Black Gate this is: "ABCD ". Note the empty character after the 'D'; this is not a space, this is a character created by holding Alt and pressing 2, 5 and 5 on your numpad.
For Serpent Isle this is: "manimal". Can be handy, because closing the Arabella's (Hawk's ship, near the Sleeping Bull) gang plank will basically end your game (unless you find a telekinesis scroll, but I don't think they exist in the first part of the game).
In-game, press F2 for the cheat menu. I think you need to press H for the hack mover. You can then basically manipulate objects that are normally unreachable, or even move solid walls.
More info about adding parameters here:
https://www.gog.com/forum/ultima_series/ultima_7_serpent_islehelp_activating_the_cheat_menu If you're using Exult, then cheats will already be activated.
Also: I really advise against using cheats, unless you know what you're doing, because you CAN break your game.
Teleporting around (F3) can 'break eggs', activating flags/triggers that shouldn't have been activated yet. And the F2 menu has the power to manipulate a lot of things, not always with good results if you don't know what you're doing.
