"How can I force the TV to connect to the WiFi without the remote?" You can't. Yes, it should have reconnected if the SSID and password hadn't changed. But since it didn't, the only way to reconnect it is with a Roku remote. Most all of the TVs support an IR remote, so you might be able to get a generic IR remote that lists Roku code support. Or borrow someone else's Roku remote.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.