Thanks nc50lc!
No problem.
The next time you open Electrum on your phone, it will still prompt you to enter a password. You can but you don't have to do that. Click outside of the window again like nc50lc explained, click the Open/Create Wallet button, select the wallet you want to load, and enter the unique password you have set for that wallet only.
Even better if it's the active wallet that he used in the last session; it'll be the first wallet Electrum will load the next time he start the app.
In that case, loading it is as simple as opening Electrum then type an easy password or similar to open the watch-only wallet.
A habit of closing Electrum while it's the "
current wallet" is recommended in that scenario.