I lost the remote to my Roku 4k express. I have used my phone as a remote but in order to connect to my device my Roku has to be on the same internet connection as my phone. And without them on the same network my phone remote will not work. So how do I change my Roku network to my phone's network without a remote
To change the Roku’s network, you’ll want a remote. Sometimes you can use the trick of setting up the new network to have the same SSID and passphrase as the previous network which allows the Roku to automatically connect. Even if you did that, I’m not sure it would work in your case because your phone may separate its hotspot network from the network that the phone itself is attached to. (ie: the Roku app on your phone and the roku device may still be on separate networks.)
@Daring_gal59, the question is do you remember the SSID/network name and password the device was connected to previously? If not, you need a physical remote. It doesn't have to be a Roku remote; many cheap universal remotes support Roku devices.