Help with Build from Source - demo traccar servers - .

Hello Every....
I'm do my first steps for build from source and I'm completely newvy.
I work/test with/under a Linux Mint Mate 64 bits installation.
I do this, I've git, I've clone Server and I've clone traccar-web or web-interface. Both in a specific folder of my system.
In the Server clone local folder I do ./gradlew assemble and Build Succesful. For now that's all because I am under cgnat and have some questions.
How I test with the demo server traccar? What file I need edit and change Domain/Ip address to test with demo demo3.traccar.org ?
Where or how I need put path the Sencha Cmd for legacy-web purposes? I've unzziped Sencha Cmd 7.0 in the Server clone folder. I've do Right?
Thanks to read me.

If you want to test the legacy we app with the demo backend, you would need a proxy. Why would you want to test with demo and not your local server?

Thanks Anton.
I am not entirely sure. I was asked by someone who is helping me in the build from source. I suspect is because I under cgnat and the future part 2 of the build from the source is about REST and Websockets and need test conections. Ok no problem, I predict that use yours demo server for that is imposible. Don't worry about demo3.traccar, I'll use one Instance Oracle to test with servers conexions.
Let me know "please" about Sencha Cmd and where install or the phat.

You just run their installer and make sure that the sencha command is available in your path.

Ok I'll try to understand you, I'm nule for Informatic but just need read.

Sorry, maybe I don't catch you. I do all process describes here. https://www.traccar.org/build-extjs/
the first part in the normal terminal with the necesary updates and the last part in the "web" folder into of my clone traccar-web

111@111-desktop:~/traccar-git/traccar/traccar-web/web$ sudo npm run build
build
sencha compile --classpath=web/app.js,web/app,node_modules/extjs-gpl/packages/core/src,node_modules/extjs-gpl/packages/core/overrides,node_modules/extjs-gpl/classic/classic/src,node_modules/extjs-gpl/classic/classic/overrides exclude -all and include -recursive -file web/app.js and exclude -namespace=Ext and concatenate -closure web/app.min.js

sh: 1: sencha: not found
111@111-desktop:~/traccar-git/traccar/traccar-web/web$ 

When I install Sencha Cmd I check YES in something about phat, I Don't remerber exactly what says.

I think you missed this part:

make sure that the sencha command is available in your path

Thanks, sure is that because i don't know what is sencha command.

Sorry, I ask. Is in my path?

111@111-desktop:~$ echo $PATH /home/111/bin/Sencha/Cmd:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin 111@111-desktop:~$

Fix It. Regards!