Stupidest router ever! But hey you get stickers with it to make it pretty! See comment below which I posted on another query....
You can change the IP address if you get into developer mode. User lost_sock posted this solution a few months ago and I can confirm it works. As an aside, I have never encountered such stupidity as to lock clients out from setting their LAN IP address and DCHP range.. And the 101 has only one LAN port as well.. Probably the worst router I've ever had to deal with....
Solution:
All the settings are hiding in developer mode. It's client side, so we can just bypass the login.
Install Charles, the trial is fine
https://www.charlesproxy.com/
Grab the config file here (101-dev-mode.xml):
https://mega.nz/file/a5ckgR4S#zuJTN_l8PXkDK7kzrOhejk-zFJd-0VP68Z9QnkTJU_0
1. Open Charles
2. Menu: Tools>Rewrite
3. Import: 101-dev-mode.xml
4. Enable Rewrite: ticked
5. Hit OK
With that running, you can go into the router config and all the hidden menu items will be unlocked.