I just tested this out on mine. I told it to forget the TCL Roku TV in the bedroom. On the next scan for devices, which it seems to do every few seconds, the TCL was located and I was given the ability to connect to it again.
This was with the android Roku app version 188.8.131.525915 on a Galaxy A42 5G.
To be found, the Roku needs to be connected to the network. If network problems were what prompted you to "forget" that Roku in the first place, you'll need to get the net connection reestablished before the app can find it. IP numbers are assigned by the router, not intrinsic to the Roku. If it's not connected on the network it doesn't have an IP to connect to.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X