A Factory Reset alone should not have removed the app
If you removed the YTTV app manually (Highlight the app/Options (*)/remove) in an attempt to resolve loading issues, you wont be able to get it back until after the Roku & Google dispute is resolved.
You can access YTTV through the YT app: load YT, select "YouTube TV" in the lower left corner of the UI.
You'll need to contact Roku CS otherwise:
chat/email/phone: https://support.roku.com/contactus (choose setup/ultra/other/need more help?)