Pinmist

Static mode sets your iPhone's location to a single place and holds it there until you reset it.

Place the pin

Choose Static in the switch at the top of the map, then do any of these:

Search. Type a place or an address and pick a suggestion. Press Enter to take the first one.
Click the map. The pin moves to where you click.
Drag the pin to fine-tune it.
Type coordinates. Edit the latitude and longitude in the panel. They take six decimal places, which is about ten centimetres.

The buttons on the right of the map zoom in and out, centre the map on the pin, or centre it on the location your iPhone is currently reporting.

Change your location

Press Change location. The button shows a spinner, then Pinmist confirms the change. Apps on your iPhone see the new location within one to three seconds.

The panel shows when the simulation began, for example "Simulating since 14:02", and the status dot turns solid green.

Change location stays greyed out until your iPhone is ready, with a green dot, and the pin is on the map.

Reset to your real location

Press Reset location. Pinmist stops the simulation and iOS goes back to GPS.

Your real location also comes back if you unplug the cable, quit Pinmist or restart the iPhone. After a reset, iOS can take a few minutes to find you again. Restarting the iPhone speeds that up.

Keep the location after unplugging

Normally the simulated location ends as soon as the cable comes out. If you need it to stay while you take the phone away:

Set the location and wait until your apps show it.
With the iPhone still plugged in, open Settings › Privacy & Security › Developer Mode and turn it off.
Unplug the cable.

The location stays until you restart the iPhone. To use Pinmist again, turn Developer Mode back on, which takes a restart.

Warning. This relies on how iOS behaves today, and Apple could change it in any update. Check your location in a maps app before you rely on it.