Android Question can i make android app that restart modem,and for your information modem supports telnet and ssh

Yes, if you can access the modem, you will be able to send ATZ command and reset the modem.

can you give me example,and what is the ATZ?
and i need to restart not reset

ATZ is the old fashioned command introduced by HAYES modems brand, and made it a standard. https://en.wikipedia.org/wiki/Hayes_command_set I am felling I am old
To dial another modem ATDT or ATDP + the number etc. golden times

I never tested in B4A, but you can use AsyncStreams to open a TCP socket to port 23 etc.

Read this :
https://www.b4x.com/android/forum/threads/problems-with-telnet.15678/#post-139335

And the tutorial of AsyncStreams
https://www.b4x.com/android/forum/threads/asyncstreams-tutorial.7669/#content

That way is using a Telnet now B4A support SSH too.