In all desktop views/browser I can hide in custom.css

.tm-footer {
background-color: #fff;
}

In mobile view on Samsung, this element still visible. Could not find the appropriated css.

Try this code:

@media (max-width: 768px) {
.tm-footer {
display: none;
}
}

In styles/green/

theme.css or bootstrap.css does not work with.
any other place possible?

Please never edit the original CSS files, because these files will be overwritten with the next theme update. Always add your custom style to the custom.css

www.joomlaplates.com/template-customizing