If you have more than one GQueues account, you can access all of them from the mobile app.

To add another account tap your profile picture in the upper right corner.

This will open app settings where you can then tap Add Account to sync another account's data to your device.

Log in with the credentials for the other account.

To switch between accounts tap your profile picture in the upper right corner.

The account you are currently viewing will be shown at the top. Select another account from the list to switch to that account.

From your account list in settings, tap the gear icon next to the account you want to remove from your device.

Then tap Remove Account. This will not delete any data - it simply removes the account from your mobile app on this device.