TL;DR: He will not be able to setup/use the Roku without a remote (WiFi Direct remote for Stick models) and a Roku account (email address).
You didnt do him any favors giving him a Roku without a remote.
Since replacement remotes for Stick models are $20-30, he should just buy a new Roku device (the Express 4K+ is on sale for $30)
You didnt mention the Roku model name or number of the Roku "stick".
This matters because actual Stick models require WiFi Direct paired remotes and non-Stick models can be used with IR remotes.
"Pairing" is linking the WiFi Direct remote to the Roku device.
"Activating" is linking the Roku device to a Roku account.
There are several "resets" available for Roku devices:
1) Restart: Settings/System/System restart/Restart
2) Network Connection Reset: Settings/System/Advanced system settings/Network connection reset
3) Factory Reset: Settings/System/Advanced system settings/Factory Reset
Best practice when giving someone else your device (assuming you DONT want them using your Roku account or streaming services' subscription account information) is to Factory Reset your device.
Its not clear from your comments whether you simply Restarted the device, or Factory Reset the device.
When you Factory Reset a Roku, it unlinks it from the Roku account it was linked to, removes all apps, and resets all the settings to their defaults.
If you Factory Reset the device, you dont need to do anything with your Roku account and the device will be automatically unlinked from it.
When setting the Roku up again, a remote is required (Stick models require a paired WiFi Direct remote, whereas other models can be setup with IR-only remotes) as well as a Roku account (email address) to link the device to.
He will not be able to setup/activate without a remote and his own Roku account (email address).
Considering the price of a new $20 Voice Remote or $30 Voice Remote Pro, he would be better off just getting a new Roku - the Express and the Express 4K+ are available for $30 (I recommend the Express 4k+) at Roku.com/elsewhere.